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AUGUST 1989 ¢ £1.25 


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PAGE 61a PAGE 35¥ 


NEXT MONTH 


Improve your workshop and enhance 
your experimenting with our triple 
function test gear project - combined 
Icd frequency counter with separate 
audio and digital logic signal 
generators. And add hi-tech security 
to your home with our sophisticated 
microprocessor controlled alarm 
system monitor. Owen Bishop will 
continue his discussion of practical 
theory in the Digital Electronics 
series, and ... well, you'll have to wait 
and see what other interesting 
features we've lined-up. They'll be 
worth waiting for, that's for sure! Start 
the count down now - it's not long till 
our next edition is hot off the press ... 


* DON'T MISS THE 
SEPTEMBER 1989 ISSUE 


* ON SALE FROM FRIDAY 
AUGUST 4TH 


* AND STILL AT ONLY 
£1.25 


* YOU CAN'T BEAT OUR 
VALUE 


* OR OUR HI-TECH GOOD 
LOOKS! 


PRACTICAL ELECTRONICS 


CONTENTS 
COMPETITIONS 








WIN THE NEW SHARP IQ ORGANISER]! ........ ce seseeessseeeeenens 61 


Sharpen up your organisational intelligence with a Sharp IQ personal electronic 
organiser. Worth £170. Three to win - just pit your wits against the Editor's authoritative 
punning! | 


TELEPOINT TELEPHONES - THE WINNERS 


Did you ring the bell in our May 89 competition? With decorum Ed's quorum drew five 
for the Forum - we've lined up the answers, so don't ignore ‘em! 


CONSTRUCTIONAL PROJECTS 


STEPPING MOTOR DRIVER by Mark Stuaft ..............sseeeeees 12 


Step into the world of robotics by adding motive power to your home micro using the 
new M5804 chip in a multimode motor module. 


HAND CLAPPER by Harvey Kent ..........cccccsssssssesseeeseesssesssees 26 


With comparative ease you can automatically applaud us for putting rhythm in your chip 
board with this handy effects box. 


EASI-BUILD CIRCUIT by John Becker 


Fancy exterminating the Doctor? Build a Vodalek voice box as this month's project and 
speak-easi like a robot. 


ro) od =O] FN od = AW OL te 


HF RADIO - PART ONE by Mike Sanders. ..............csssseceeeeeees 19 


Wave upon wave, layer upon layer, electromagnetic radiation randomly fills the 
universe - yet from chaos we seek order and communication, and achieve them! How? 
We examine the principles. 


BOATING REVOLUTION - CONCLUSION by John Becker .35 


Monitoring your craft's precise position is greatly simplified by the new generations of 
satellite-linked microterminals. 


ENCRYPTION - PART TWO by Mike Sanders ...........::csssee 39 


How the modes and standards of data encryption enhance electronic security for 
personal and corporate communications and finance. 


REGULAR FEATURES 





EDITORIAL by John Becker - Home automation update... oe 9 
LEADING EDGE by Barry Fox - Mac scrambling..........::ecceseeeeeeeeee 8 
SPACEWATCH by Dr Patrick Moore - The New Technology Telescope 46 
INDUSTRY NOTEBOOK by Tom Ivall - CIM and Society ...............0 57 
READERS' LETTERS - and a few answe's ...........cccccceeceeeeteteereeee 30 
PRODUCT FEATURES 

MARKETPLACE - what's new, where and when .........ccccceeeseeseeeeeeeeeees 4 
ARMCHAIR BOOKSHOP - a haven for practical bookworms ............. 58 
PCB SERVICE - professional PCBs for PE Projects . .........ccccceeeeeeees 60 
BAZAAR - Readers' FREE advertising Service . ...........ccceceeseeteeteeteeeees 52 
ADVERTISERS' INDEX - locating favourite stockists .........ccceeeeeees 62 


PE TAKES TECHNOLOGY FURTHER - BE PART OF IT! 


PRACTICAL ELECTRONICS AUGUST 1989 


3 








FRAME 





he imagewise/pc real-time 

Video digitiser/display board 
can digitise any NTSC, PAL or 
SECAM video source. It has a wide 
potential in industrial, security and 
desk top publishing applications. 

The system can grab a single video 

frame and digitise it to a resolution of 
256x255 with 256 grey levels. The 
board provides composite video 
output and digitised pictures can also 
be shown on an ega or vga monitor. A 
digitised picture, grabbed or software 
generated, can be applied as a caption 
or mask on a live video signal. 


The board comes with a generous 
complement of free software, giving 
advanced image enhancement, 
overlay and split screen capabilities. 
Digitised images are compatible 
with paint and desktop publishing 
programs. Sophisticated ZIP 
software enables these images to be 
modified, enhanced, filed, displayed 
and printed. 


For more information contact: 
J.B. Designs & Technology Ltd, 15 
Market Place, Cirencester, Glos, 
GL7 2PB. Tel: 0285 68122. 


FUSED 
FOR 
SAFETY 


Ss part of their current safety 

T campaign, TMK Instruments 
have announced the availability of 
fused test prods. Designed and 
manufactured in the UK the new 
prods are compatible with most test 
and measuring equipment. Safe and 
reliable, they comply with the 
requirements of the Health and 
Safety Executive and the Electricity 
Council's Engineering 
Recommendation Standards. 

Manufactured using a tough, high 
impact nylon casing both the red and 





black prods have moulded finger 
grips and guards for additional 
safety. Internal contacts, assemblies 
and tips use solid brass, phosphor 
bronze and silver plating. The 4mm 
banana plugs have safety shrouds 
with a smooth spring loaded action 
which helps when changing over to 
the moulded crocodile-clips. Easy 
multi-turn access to the fuse 
assembly allows simple replacement 
of the recommended 500mA fuse. 
Supplied as a pair in a plastic wallet, 
these fused probes offer the user a 
safer working environment. 

The price of the fused test prods, 
in a wallet, is £24,95 excluding vat. 
(Croc-clips are available at an extra 
cost.) 

For further information please 
contact Mike Dixon of TMK at 
Building 3, GEC Estate, East Lane, 
Wembly, Middx, HA9 7PJ. Tel: 01- 
908 3355. 


‘CATALOGUE 


DATABASE 


We have recently received the 
following literature: 


We've been inundated with catalogues from many of our 
advertisers - we start them here in alphabetical order, and shall 
continue next month. 


Barrie Electronics specialise in transformers and _ allied 
products, with a range exceeding that shown in their usual advert. 


They will also wind transformers to your specification if they 
don't already have one to suit you straight off the shelf. In addition, | 
they have a good range of components available, including 
semiconductors, resistors, pots, capacitors and connectors. And 
don't overlook the range of transmitting and receiving valves 
stocked, nor the very wide selection of workshop tools. Boat 
owners will be especially interested to know of Barrie's Powerverter 
dc-ac marine inverters. Barrie Electronics Ltd, Unit 211, Stratford 
Workshops, Burford Road, London E15 2SP. 01-555 0228. 

J and N Bull's catalogue has always been an Aladdin's cave of 
fascinating products. The range is too great to even cover briefly, 
but I'll highlight a few interesting items - acoustic chamber, battery 
operated laser, electronic spaceship, gardener's friend (time and 
temp module), 12V siren, ioniser for cars, golf trolley charger, and 
so it goes on .... Ask for your own copy of the amazing offerings 
and bargains from J and N Bull Electrical, 250 Portland Road, 
Hove, Sussex, BN3 5QT. 0273 734648. 

On a personal note, I am sorry to learn that Jessie Bull has 
decided to retire. I've known for some time that he has been 
considering it, but he has announced in the newsletter he sent me 
that he is actively looking for someone to take over the business. 
For anyone with the right interest, and the willingness to make a 
capital investment, taking over the business should be a most 
rewarding opportunity. Jessie Bull has been in the surplus 
electronics business for around 43 years and during that time has 
made many friends in the trade. I hope that he readily finds one of 
those friends to take over from him. If anyone is interested, give 
him a personal call in the afternoons, preferably after 4pm, on 
0273 734648. 





PRACTICAL ELECTRONICS AUGUST 1989 





EQUA 









HARMONY 


he introduction of a Dynamics 

Processor module and remote 
panel to the Harmonia Mundi 
BW 102 system, further extends its 
creative capabilities. This new 
addition offers the comprehensive 
digital audio processing functions of 
level (mixing) control, parametric 
equalisation, compression, limiting, 
expansion, noise gate and reverb 
functions. 

With the new module, a wide 
range of attack/release times are 
possible. The release time can be set 
manually or automatically, with the 
automatic function permitting the 
choice of two different releases 
times, for fast peaks and mean level. 

A unique feature of the 
BW 102/34 dynamics processor is its 
pre-delay function. The pre-delay, 
again set manually or automatically, 
enables the processor to look into 

future time, anticipating level 


DEMAND 


B .K. Electronics have at last 





succumbed to a real demand to 
case their OMP mono mos-fet 
chassis amplifiers, and have started 
by casing their MF100 and MF200 
medules. 

The new cased amplifiers will be 
known as the CA110 and CA210 
slave amplifiers. All the advanced 
features of the mos-fet chassis 
amplifiers, including the toroidal 
transformer power supply, have been 


BK. ELECTRONICS ——— 
VRE 


changes, thus avoiding overshoots 
and distortion. 

Automatic level compensation is 
also provided to make life easier 
during mastering and post 
production. 

F.W.O. Bauch, who, you probably 
know, handle Revox products as 
well, have already delivered five 
tailor-made BW102 systems over the 
past few months to CBS Studios 
London, Fine Splice Limited, 
Battery Studios, Townhouse Studios 
and Audio FX Camden. All of the 
systems include processing with 
equalisation and all systems have 
been installed in mastering suites, 
while the unit held by Audio FX is 
available for hire purposes. 


CONTACT: E.W.O. Bauch Limited, 
49 Theobald Street, Boreham Wood, 
Hertfordshire, WD6 4RZ. Tel: 01- 
953 0091 


NG CASE 


retained. These features have been 
combined with a led vu meter and an 
input level control, and are housed in 
a purposely designed black anodised 
aluminium case. 

Both amplifiers have an input 
sensitivity of 500mV for full power 
output. The CA110 provides 115 
watts into 4 ohms and 105 watts into 
8 ohms, whilst its larger brother 
boasts 215 watts into 4 ohms and 
150 watts into 8 ohms (AI power 





PRACTICAL ELECTRONICS AUGUST 1989 





If you are organising any event to do 
with electronics, big or small, drop us a 
line — we shall be glad to include It here. 


No reference tel. known. 
Jul. 24-26. 


408 0111. 





01-940 4625. 


722687. 


Centre. 01-948 5166. 





614671. 





being watts rms). The power 
bandwidth (-3dB) is 1Hz-50kHz. 
Both models are realistically priced 
at £79.00 + £4.00 P&P for the CA 
110 at £99.00 + £5.00 P&P for the 
CA210, inc. vat. 

The amplifiers are available direct 
from B.K. Electronics, Unit 5, 
Comet Way, Southend On Sea, 
Essex, SS2:6TR. Tel: 0702 527572. 


SAFE 
CLIPPING 


he new LC-160 logic clip from 

OK, said to be the first 
electrostatic discharge safe logic 
monitoring instrument, will 





Please note: Some events listed here may be trade or restricted 
category only. Also, we cannot guarantee information accuracy, 
so check details with the organisers before setting out. 


Jul. 10-13 EWEC '89. European wind energy conference and 
exhibition. Scottish Conference and Exhibition Centre, Glasgow. 





Vacuum Microelectronics — 
Conference. Bath. Contact Dr R.A. Lee, GEC Hirst Research 
Centre, Wembley, Middx, HA9 7PP. 01-908 9000. 


Aug. 25-Sep 3. International Audio and Video Fair. Berlin. 01- 





Sep. 4-6. Eurobus 89 — UK Conference. Novotel Hotel, London. 





Sep. 12-14. Optical Systems. Ramada Inn, London. 


Sep. 12-15. EPOS 89. The World's largest exhibition of retail 
information systems. Alexandra Palace, London. RMDP. 0273 


Sep. 26-28. British Laboratory Week 89. 
Computer Aided Sciences. Olympia, London. 





Oct. 16-20. Systems, Computers and Communications. 11th 
International Trade Fair and Congress. Munich Trade Fair 





Oct. 24-26. Sensors and Systems — International Transducer 
Exhibition and Conference. Wembley Conference Centre. 0822 





Nov. 7-11. Productronica. 8th International Trade Fair for 
Electronics Production. Munich Trade Fair Centre. 01-948 5166. 























2nd_ International 








Incorporating 


simultaneously monitor up to 16 
pins. Functioning as a logic monitor 
and ic test clip it is a convenient 
circuit troubleshooting tool. Its logic 
threshold is 1.5V +/-0,34V and 
voltage range is 3.5-1.5V Bandwidth 
is |MHz and current load 11mA. 

For further information 
contact: OK Industries UK Ltd, 
Barton Farm Industrial Estate, 
Chickenhall Lane, Eastleigh, Hants, 
SOS 5RR. Tel: 0703 619841. 

















arta 


DEBORAH'S 
TRIBUTE 


eborah Gardner, aged 17, of 

Whickham Comprehensive 
School in Gateshead, is pictuered 
with her YEDA trophy and her 
school's new Texas Instruments 
desktop publishing installation. She 
won them both for producing the 
most commercially viable project in 
the 1988 Young Electronic Designer 
Awards. Her project was an 
electronic time teaching aid for 
primary school children. 

With less than a month to go the 
deadline for 1989 entries, 
Whickham's headmaster Bill Smith 
invited Texas Instruments’ corporate 
communications manager, Richard 
Mann, to inaugurate the prize 
installation and address sixth- 
formers on the importance of 
electronics in everyday life and the 
exciting career prospects offered by 
the world of electronics. Most 
importantly however, the special 
assembly was called to enable the 
school to formally acknowledge 
Deborah's achievement in winning 
this major national prize. 


AVO MONITORING 
RAC 


ll of the RACs nationwide team 
of roadside patrolmen are to be 
equipped with the latest AVO M2005 
analogue/digital multimeters as part of 
the organisation's plans to combat the 
rising number of electrical breakdowns. 
As many as 1150 patrolmen will 
be issued with the instrument as part 
of a two-year programme associated 
with recruit and refresher training. 
The move comes as the level of 









Organised by the YEDA Trust, a 
registered charity, under the 
chairmanship of Professor John 
Eggleston and sponsored jointly by 
Cirkit Holdings PLC and Texas 
Instruments Ltd, the Young 
Electronic Designer Award scheme 
was recently acknowledge by the 
CBI's Director General, John 
Banham, for its impressive 
contribution in encouraging young 
people to combine technical skills 
creatively with an appreciation of the 
commercial demands of the 
marketplace. 


For further information contact: 
The YEDA Trust, 24 London Road, 
Horsham, West Sussex, RH12 1AY. 
Tel: (0403) 211048. 





electrical faults approaches 70 per 
cent of all breakdowns on British 
roads — a trend reflecting the 
increasing sophistication of modern 
vehicle electrical/electronics systems. 

On of the key requirement was that 
the instrument should be rugged and 
weatherproof. The meter includes 
built-in casing buffers to resist break- 
age and incorporates probe holders to 
allow genuine single-handed use — 
vital in roadside applications. 

The combination of a high 
resolution, dynamic pointer and 
digital displays provided the RAC 
with an unexpected bonus. The clear 
digital read-out in 10.5mm high 
numerals has enabled them to use the 
meter to interrogate the computer- 
based Electronic Control Units 
(ECU's) found on many modern cars. 
CONTACT; Kate Grenshaw, 
Megger Instruments Limited, 
Archcliffe Road, Dover, Kent, CR17 
9EN. Tel: 0304 202620. 


OPTICAL 
POLE 
VAULT 


he equivalent of 25,000 
simulataneous telephone 
conversations have been carried over 
a single optical fibre link in British 

Telecom's network, in a record- 
breaking demonstration of a 
technique which offers even bigger 
increases in capacity in the future. 

The demonstration was carried 
out on a fibre in the optical 
submarine cable between the 
Cumbrian coast and the Isle of Man. 
The system, which came into service 
last summer, operated without 
regenerators over its entire 94km 
length. 

British Telecom is the first to use 
optical wavelength division 
multiplexing over its operational 
network, by sending light at 
different "colours" or frequencies 
simultaneously along the same hair- 
thin optical fibre. 

The microchip lasers, which 
produce the separate light outputs at 
slightly different wavelengths, were 
developed by British Telecom 
scientists at the company's research 
laboratories at Martlesham Heath, 
near Ipswich. 

Dr Tom Rowbotham, Director 
Network Technology at the 
laboratories, explained: "The 
research team combined the outputs 
of these lasers to feed one of the 
fibres in the cable. The wavelength 
spacing of the four separate outputs 
was significantly closer — by an 


| order of magnitude — than that 


achieved in earlier trials of 
wavelength division multiplexing. 

"This is the first time that WOM 
has been used in the field using fully 
packaged and commercially 
available components. The 
demonstration was part of British 
Telecom International's assessment 
of the impact of new technologies on 
future submarine systems. 

"It will enable such systems to be 
readily upgraded in the future at 
minimum cost to provide direct 
increases in capacity. And this 
benefit will apply with equal force to 
longer systems incorporating optical 
amplifiers, which are able to handle 
multiple transmissions without 
difficulty." 

For those of you who have a 
craving for hi-tech facts and figures: 
The Isle of Man cable contains six 
pairs of fibre, each singlemode 
operating in the 1,550nm band, at 
which the end-to-end transmission 
loss is -27dB. Currently five pairs 
are in commercial service, each 
operating at a direct detection line 
rate of 140 Mbit/s, which gives a 
capacity of 1,920 telephony 





channels per fibre pair. 

In the experimental transmission, 
the laboratory staff used four 
distributed feedback lasers operating 
at 1,525, 1,536, 1,546 and 1,557nm 
respectively. One laser was 
moulded at 140 Mbit/s, the other 
three at 565 Mbit/s, all four outputs 
being multiplexed onto a single fibre 
using a combination of passive and 
wavelength-sensitive fibre couplers. 

After transmission through the 
fibre the four signals were separated 
at the receive end using a 
commercially available, singlemode, 
fibre-tailed grating demultiplexer, 
each laser wavelength being 
temperature tuned to the centre of 
the grating pass band. 

The operation of three channels at 
565 Mbit/s and one at 140 Mbit/s 
increased the capacity of the system 
by 13 times, to 24,960 telephone 
channels. This was equivalent to 
operating the complete fibre system 
at 1.8 Gbit/s. 

And just as a side-line story, BT 
offered engineering training to 
Scottish telephone operators when 
the Dumphries operator service 
switched to Ayr as part of a 
Modernisation programme. The 
picture shows five of the "Hallo- 
Girls" who followed up the call. 
They're now top of the pole in our 
headlines! 





SAFETY AT 
WORK 


W ith health and safety at work 
receiving greater attention 
than ever before, TMK Instruments 
have introduced a new portable 
appliance tester. Designed and 
manufactured in the UK, Model TEM 
4600 can be used by non-technical 
personnel after brief training. Ideal 
for suppliers, hirers and users to 
check the electrical safety of 
appliances, tool, equipment and 
extension wiring for compliance with 
the Health & Safety at Work Act. 
Two fault simulators are supplied for 
carrying out regular self checks, one 
for earthed appliances, the other for 
double insulated class II devices. 
CONTACT: TMK Instruments, 
Building 3, GEC Ind. Estate, East 
Lane, Wembley, Middx, HA9 7PJ. 





PRACTICAL ELECTRONICS AUGUST 1989 














EPR Ov 
WIPEOUT 


wo versions of J.P. Designs’ 

new eprom eraser are 
available, with or without switch 
selectable timer. The basic 
construction is the same for both 
versions: an anodised aluminium 
unit, featuring a sliding drawer 
section with high density anti-static 
foam into which the eproms are 
placed for erasing. It is possible to 
erase upto 40 eproms at one time 
and when the drawer is closed it 
becomes almost light tight. 

Erasing is performed by a lower 
power 6 watt lamp, which keeps the 
unit cool whilst emitting the correct 
light level to the eproms. Erasing 
takes between 20 and 30 mins. The 
unit is compact at 320 x 87 x 60mm 
and the tube is totally enclosed. All 
units are supplied with 1 metre 
mains cable and lamp fitting 
instructions. The timer version also 
features an led indicator and times of 
10, 20 or 30 mins can be selected. 
For your safety the casing is earthed 
and carries a warning label. 

These erasers are available at the 
low cost of £54.95 for the basic 
version and £64.95 for the timer 
version. 

For further information contact: 
J.P. Designs, The Old School, 
Prickwillow, Ely, Cambridgeshire, 
CB7 4UN. Tel: 035 325/455. 


PHAX- 
SWITCH 


he latest product from The Switch 
Electronics stable is the BIT 
PHAXswitch which enables a phone 
and a fax to operate, problem-free, on a 
single telephone line. Thought to be 
ideal for small businesses or use at 
home, the unit is convenient, fully 
automatic and cost effective. 
Convenient, because it can be 
installed in seconds by the user (no 
waiting for the telephone company 
to install a new line) and because it 
can be easily moved from one 
location to another. Taking work 
home at the weekend? Simply take 
your fax and PHAXswitch with you. 
Automatic, because it is able to 





identify whether an incoming call is 
from a fax machine wishing to 
transmit or a person wishing to 
speak — and directs the call 
accordingly. Calls from non- 
automatic fax machines are also 
accommodated — in most ingenious 
and simple manner. After two rings 
the caller is greeted with a friendly, 
digitised voice which says: "This is 
a BIT PHAXswitch answering your 
call. If you wish to send a fax, 
please say 'fax' after the tone. 
Otherwise, please wait until the 
phone is answered." A time delay of 
three seconds, for the caller to say 
‘fax’, is utilised to determine which 
way the call should be directed. 

The PHAXswitch can also be 
used in manual modes; for example, 
when a call from a friend is expected 
and the user does not wish him to be 
greeted with the recording message. 
Comments Steven Wickens of 
Switch Electronics: "This new 
device provides an invaluable 
automatic switch-over for fax 
machines and dramatically increases 
the scope of a single telephone line. 
It's no wonder that the BIT 
PHAXswitch walked away with the 
1988 Best New Product award in its 
category at the prestigious Telecom 
Asia exhibition in Hong Kong." 

For details of the further benefits of 
the PHAXswitch contact Switch 
Electronics, 241 Desborough Road, 
High Wycombe, Bucks, HP11 2QW. 
Tel: 0494 463532. 





SSS 


VISIOMATION 


new company has been formed 
T specifically to provide image 
processing modules and systems for 
education and others who wish to 
learn about machine vision. 

Their first product is a complete 
image processing system based on 
the BBC microcomputer. Despite its 
low price of £365 it is complete (less 
the BBC, of course) with all the 
facilities of far more expensive 
system. Included are a camera, 
interface, comprehensive software 
and a very comprehensive 
instruction manual. 

The system is based on one that 
has been developed over the last few 
years by Leicester Polytechnic, 
specifically for teaching image 
processing and machine vision to 
non-specialist students. 


PRACTICAL ELECTRONICS AUGUST 1989 





CHIP COUNT 


This month we highlight the new TL030 and TLOSO series of 
enhanced jfet-input opamps introduced by Texas Instruments. 
They are of immediate relevance to many PE readers since the 
chips are improved and direct replacements for the familiar 
TL060, TLO70 and TL080 series. 


TLO3SO AND TLOSO OPAMPS 


With the introduction of the first bifet family in the late 1970's, 


jfet-input opamps have become firmly established as low cost, high 


speed amplifiers. 


In applications where dc precision, in addition to ac performance 
is required, a trade off generally exists between the two. Texas 
Instruments, with its advanced design and processing, believes it 
has solved the problems of dc precision in bifets with the release of 
the TL030 and TLOSO series. The new bifets combine, and even 
improve on, the excellent slew rates of the first generation bifet 
devices with a step function improvement in dc precision. 


Bifets employ junction field effect transistors in the differential 
input stage of what is in effect a bipolar opamp. The result is 
higher slew rates and lower input bias currents that bipolar 
opamps. System designs using jfet-input opamps generally rely on 
these two key parameters: high slew rates for good ac performance 
and low bias currents for high impedance interfacing. 


Many applications require both good ac performance and steady 
state precision. Bipolar opamps can offer excellent dc precision in 
terms of input offset voltage (Vio) and gain, but at the expense of 
ac performance. Furthermore, jfet-input opamps with good dc 
precision have been especially difficult to produce as a result of 
shifts in Vio caused by package induced stress. Existing bifet 
technology opamps, when assembled in plastic such as the familiar 
dual-in-line package, typically exhibit a 300 microvolt shift in Vio, 
often moving Vio out of specification. 


For this reason TI has, over the last few years, evaluated the 
possibility of a low offset bifet while retaining the characteristic ac 
performance. The result is the new TLO30 and TLOS50 series. The 
new bifets are also more stable with time - in precision 
applications drift with time can cause significant problems and 
result in continual recalibration. The new designs have reduced the 
300UV average shift down to 60LV. 


Unity gain bandwidths remain unchanged, with between a 25% 
to 85% increase in slew rate for the TLO50 series when compared 
with the TLO70 series. The TLOSO series are improved versions of 
the TLO70 and TLO80 series, and the TL030 series are improved 
versions of the low power TL060 series. They are all plug-in 
replacements. 


For further information contact: Texas Instruments Ltd, 
Manton Lane, Bedford, MK41 7PA. Tel 0234 270111. 





It is ideally suited for those people 
who wish to obtain a practical 
insight into machine vision for 


automated inspection, machine 


control, surveillance, etc, without a 
big investment in cash or time. The 
comprehensive instruction manual 
will lead even those with a 
superficial experience of 
microcomputers through the subject 
quickly and easily. No knowledge of 
programming is necessary. Despite 
its simplicity, it is capable of 


achieving real results with practical 
machine vision problems. 

By the time this information goes 
to press. Visiomation expect to 
introduce a range of STE modules, 
starting with a 256 x 256 
Framestore, and a video input and 
output module. 

CONTACT: Visiomation Ltd, Unit 
12, Lyons Farm Industrial Estate, 
Lyons Road, Slinfold, Horsham, W. 
Sussex, RH13 7QP. Tel: 0403 
790988. 













t does now look as if the firms trying 
iT: sell the idea of satellite to the 

British public may fail, with 
catastrophic cash losses all round. Much of 
the damage is self-inflicted. Instead of 
joining forces to try and educate the public 
on a very muddled field of new technology, 
rival factors have fought in public and 
created even more confusion. 

This is the current state of play. When 
(if?) launched this autumn, BSB's satellite 
will hang at a completely different place in 
the sky from the Astra satellite which 
already carries Sky and W H Smith (31 
degrees West for BSB, 19 degrees East for 
Astra). One aerial cannot pick up both 
signals, unless it is an expensive and 
difficult-to-install beast which moves under 
remote-controlled motor power. In most 
cases it will be easier and cheaper to have 
two aerials, or use one aerial and forget 
about the other service. 

BSB will use a completely different trans- 
mission system from Sky, D-MAC instead of 
PAL. BSB will also use a different scram- 





MAC SCRAM 


bling more accurate, encryption system from 
Sky, Eurocypher instead of Videocrypt (pre- 
viously called Palcrypt). Eurocypher was 
developed by General Instruments, in the 
USA, from the Videocypher system which 
is the defacto standard in North America. 


EUROCHYPT 


W H Smith still threatens to switch from 
PAL to D-MAC and adopt yet another 
scrambling system, called Eurocrypt. 

This had prevented the owners of the 
Astra satellite from launching a generic 
advertising campaign for all programmes 
available from the same source. 

BSB will only supply its descrambling 
equipment to four selected suppliers of BSB 
receivers — Ferguson, Philips, Tatung and 
Salora. So Sky receivers made by other 
firms cannot be modified to receive BSB. 
This is why the Evening Standard cancelled 
its competition with supposedly "future- 
proof" Grundig receivers as prizes. 

So, the total kit needed to receive all 
programmes promised for the end of this 
year becomes an absurd two aerials and 
four set-top boxes costing up to £1000 to 
buy and install, and gobbling subscriptions 
at the rate of around £30 a month. Because 
there is no agreed electrical interface 
standard between dishes and receivers, it is 
impractical to mix and match. 

Compare that with the price of a BBC tv 
licence (£66) and the simplicity of a 
conventional tv aerial and video recorder. 

A full eight months after BSB scored 
extensive publicity by unveiling its squarial 
flat dish aerial (without actually explaining 
that it was only unveiling a wood and plastic 








BY BARRY FOX 
Winner of the 
UK Technology Press Award 


Satellite TV - 
will it end up in 
the crypt, or just 
turn out to be a 
cypher? 





dummy) the company had still not demon- 
strated a working prototype to the trade and 
press or placed manufacturing contracts. 

BSB still pledges a full receiver kit for 
£250. In Japan, where there is already a 
DBS service, flat plate aerials cost more 
than that on their own. 





FIXING LIMITS 


Whatever the shape of the aerial, diy 
dish fixing is to be recommended only to 


electronics hobbyist. Even then it is 
downright dangerous to learn by trial and 
error how to connect, align and then secure 
an aerial on a high ladder or sloping roof. 
Although the government has ditched its 
scheme for a £10 dish licence, because it 
cost more than £10 to process each piece of 
paper, the Department of the Environment's 
planning regulations set a limit of one dish 
(of less than 90cm) per building. The 
Home Office's Cable and Broadcasting Act, 
1984 flies in the face of this. The Cable 
Authority is duty-bound to enforce clauses 








BLING 


in the Act which make it a criminal offence 
for even two flats to share a dish without 
becoming a licensed cable station. 


DUTCH COURAGE 





When Philips signed with BSB, in 
February, to become the fourth supplier of 
set-top D-MAC receivers, the Dutch com- 
pany was put in a very difficult position. 
The position got even worse when, less than 
a month later, Philips signed to supply 
descrambling equipment for Sky too. 

The decisions were pragmatic and 
commercially sound. Unfortunately they 
were covered in face-saving fudge which 
only adds to the general confusion. 

The original MAC system (C-MAC) and 
the British variant to be used by BSB (D- 
MAC) will not work on the Continent, 
because the eight channel digital sound 
signal has too broad a bandwidth to be 
distributed by their extensive cable systems. 









This is why Philips has so far backed D2- 
MAC, which was half the number of sound 
channels and half the bandwidth. 

Two years ago Philips and Thomson 
(with software company Logica) formed the 
Euromac consortium to develop a scram- 
bling and encryption system for MAC. In 
1988 it crystallised into Eurocrypt. The 
decoder is controlled by a smart card (credit 
card with built-in computer). This is the sys- 
tem W H Smith plans to use with D-MAC. 

Fearing delays in availability of the vital 
chips, BSB signed with ITT Intermetall to 
produce D-MAC chips and with General 
Instruments in America to_ provide 
Eurocypher encryption modules. 

But Philips cannot bear to admit the 
hard truth — that it has had to turn against 
both D2-MAC and Eurocrypt, and use D- 
MAC and Eurocypher instead. With 
unbounded optimism Philips satellite boss 
Peter Groenenboom has told the UK 
Government what it should do; adopt a 
common MAC standard and a common 
scrambling system by January Ist 1991. 

This is technical nonsense, as well as 
astonishing cheek. 

The Eurocrypt and Eurocypher systems 
are quite different. Whereas Eurocrypt needs 
a smart card reader in the receiver, Euro- 
cypher sends all the necessary decoding and 
subscription validation signals over the air. 
And there is no compatibility between 
dedicated D and D2-MAC systems. 

Now Philips has signed with Sky to 
produce the PAL Videocrypt decoders which 
will be needed to receive scrambled movies. 

Quite simply everyone in the satellite 
game is betting on all competing systems — 
which could simply ensure that none of 


them win. rE 


PRACTICAL ELECTRONICS AUGUST 1989 











n the April and May issues | 

reported on the Home Automa- 

tion conference held in London 
during December 1988. Since then, 
the organisers, RMDP Ltd and the 
National Economic Development 
Office, have continued their re- 
search into consumer reaction to the 
concept of home automation. Their 
130-page updating report released 
at the end of May makes interesting 
reading. 

To summarise briefly, the most 
important issues raised by consu- 
mers relate to reliability, control, Big 
Brother, familiarity, isolation and 
loss. The first of these, reliability, is 
a principle concern among those 
questioned, and is a factor to which 
manufacturers must pay consider- 
able attention. Although it is appar- 
ent that consumers expect change 
and do not resist it, their reserva- 
tions about home automation are 
based upon their experience of 
unreliability in computers and other 
complex machines at work. 

The research shows that consu- 
mers expect to be given much better 
control over domestic equipment, 
and that automated systems must 
be designed to be flexible. It is par- 
ticularly important that any applian- 
ces forming part of a complex 
system must be able to operate on 
their own even if there is fault else- 
where in the system. (| wholeheart- 
edly endorse that since at the time 
of writing there is a peculiar electri- 
cal system problem in my own home 
which | have not yet resolved!) The 
report summarises that "it is ex- 
tremely important to consumers that 





PRACTICAL 


ELECTRONIC 


Alters 


EDITORIAL | 


they continue to be in charge of 
what goes on in their homes". 

The Big Brother concept is of 
concern to me, and is obviously of 
concern to many others, particularly 
those who are better informed about 
computer- based systems. The fear 
is that home automation will permit 
invasion of privacy. Consequently, 
the report concludes that collation 
of and dealing in information deri- 
ved from home-based transactions 
may need strict regulation to fore- 
stall consumer resentment and fear. 
| for one am unclear as to how the 
Data Protection Act currently ap- 
plies to telebanking, teleshopping 
etc. 

Fear of the unknown is a com- 
mon human condition, and is a 
factor to be addressed regarding 






home automation products and 
services. If these can be presented 
in such a way that they can be 
perceived as an extension of some- 
thing with which consumers are 
already familiar, they are more likely 
to be accepted. The same is true if 
they provide a solution to an al- 
ready recognised problem. The 
report rightly concludes that percep- 
tion that an item falls into one of 
these categories can have a major 
effect on its evaluation. In this 
context, familiarity is likely to breed 
contentment, not contempt. 

Another issue highlighted is that 
home automation arouses concern 
among many consumers about a 
deterioration in the quality of their 
lives. The reason given is that 
passivity, isolation, de-skilling and 
atrophy of mental and imaginative 
functions are all to some degree 
feared. This, to me, is indeed an 
unexpected finding. One of the 
primary motives for introducing 
automation to the home is surely to 
enhance one's life style. That has 
usually been the case presented for 
many domestic devices, and it 
seems reasonable to extend that 
case to include the newer concepts 
emerging under the general title of 
home automation. 

Although | cannot overlook the 
profit motive driving manufacturers 
concerned with this infant technol- 
ogy, | am convinced that there will 
be true benefit to society in general 
arising from widespread implemen- 
tation of home automation. 


THE EDITOR 





Editor: 
John Becker 
Sub-Editor: 
Helen Armstrong 
Technical Illustrator: 
Derek Gooding 
Advertisement Sales: 
Sarah Holtham 
Business Manager: 
Mary-Ann Hubers 
Circulation: 
David Hewett 
Publisher: 
Angelo Zgorelec 
Editorial and Advertising Address: 
Practical Electronics, 
Intra House, 193 Uxbridge Road, 
London W12 9RA 
Tel: 01-743 8888 
Telecom Gold: 87: SQQ567 
Fax: 01-743 3062 


Advertisements 
All correspondence relating to advertise- 





ments, including classified ads, should be 
addressed to: The advertisement depart- 
ment, Practical Electronics, at the above 
address and telephone number. 


Readers’ Enquiries 

All editorial correspondence should be 
addressed to the editor and any letters 
requiring a reply should be accompanied by 
a stamped addressed’ envelope, or 
equivalent payment. 

We regret that lengthy technical enquiries 
cannot be answered over the phone. 


Subscription Address: 
Practical Electronics, Subscription Dept., 
P.O. Box 500, Leicester LE99 OAA. 


Annual Subscription Rates: 
U.K. £15.00 Overseas £18.00 


Cover Illustration 


Mark Taylor 
© Intra Press 1989. Copyright in all 
drawings, photographs’ and _ articles 


published in PRACTICAL ELECTRONICS is 
fully protected, and reproduction or imitations 
in whole or in part are expressly forbidden. 
All reasonable precautions are taken by 
PRACTICAL ELECTRONICS to ensure that 
the advice and data given to readers is 
reliable. We cannot, however, guarantee it, 
and we cannot accept legal responsibility for 
it. Prices quoted are those current as we go 
to press. All material is accepted for 
publication on the express understanding 
that the contributor has the authority to 
permit us to do so. ISSN 0032-6372 


Published on Ist Friday of each month by Intrapress, 193 Uxbridge Road, London W12 9RA. Typesetting, artwork and film by Gilfillan Ltd. Mitcham, Surrey and printed in England by McCorquodale Magazines 
Ltd. Andover, Hants. Distributed by Seymour Press 01-679 1899. PRACTICAL ELECTRONICS is sold subject to the following conditions, namely that it shall not, without the written consent of the Publishers 
first having been given, be lent, resold, hired out or otherwise disposed of by way of Trade at more than the recommended selling price shown on the cover, and that it shall not be lent, resold, hired out or otherwise 
disposed of in a mutilated condition or in any unauthorised cover by way of Trade or affixed to or as part of any publication or advertising. literary or pictorial matte’ whatsoever. 


PRACTICAL ELECTRONICS AUGUST 1989 





01-205 9558 TECHNOMATIC LTD Lrp 01-205 9558 





BBC Computer & Econet Referral Centre 


AMB15 BBC MASTER £346 (a) 
AMC06 Turbo (65C — 02) Expansion Module 


ADCO8 = 512Protessor £195 (b) 
ADF14 = Rom Cartridge £13 (b) 
ADJ22 ~— Ref Manual Part 1 £14 (c) 


BBC MASTER COMPACT 
A free packet of ten 3.5° DS discs with each Compact 


AMB12 BBC MASTER Econet £315 (a) 


... £99 (b) 
ADJ24 = Advanced Ref Manual ..... .. £19.50 (c) 
ADF10 ~~ Econet Module .... £41 (c) 


ADJ23. RefManualPartll £14 (c) 
BBC Master Dust Cover £4.75 (d) 


SYSTEM 1 128K Single 640K Drive and bundled software £385 (a) 
SYSTEM 2 System 1 with a 12° Hi Res RGB Monitor £469 (a) 
SYSTEM 3 System 1 with a 14” Med Res RGB Monitor £599 (a) 
Second Drive Kit £99 (c) Extension Cable for ext 5.25 drive £12.50 (d) 


View 3.0 User Guide £10 (d).... 

BBC Dust Cover £4.50 (d) 

ADFS ROM (for B with 1770 DFS & B Plus) £26 (d) 
ACORN Z80 2nd Processors £329 (a) 


....... Viewsheet User Guide £10 (d) 
1770 DFS Upgrade for Model B £43.50 (d) 
1.2OS ROM £15 (d) 


ACORN 6502 2nd Processor £173 (b) 





































MULTIFORM Z80 2nd Processor £289 (b) 
TORCH Z80 2nd Processor ZEP 100 , eee 
TZDP 240: ZEP 100 with Technomatic PD800P dual drive with built-in monitor stand 


.. ACORN IEEE Interface £269 (a) 
... £229 (a) 
. £439 (a) 


META Version Ill — The only package available in the micro market that will 
assemble 27 different processors at the price offered. Supplied on two 16K 


roms and two discs and fully compatible with all BBC models. Please phone 
for comprehensive leaflet £145 (b). 


We stock the full range of ACORN hardware and firmware and a very wide range of other 
peripherals for the BBC. For detailed specifications and pricing please send for our leaflet. 


PRINTERS & PLOTTERS 


EPSON STAR NL10 (Parallel Interface) 
EPSON LX86 STAR NL10 (Serial Interface) 
STAR Power Type 


BROTHER HR20 


COLOUR PRINTERS 


LQ800 (80 col) 
LQ1000 


TAXAN 
KP815 (160 cps) 
KP915 (180 cps) 


Dotprint Plus NLQ Rom for 
Epson versions for FX, RX, MX 


and GLP (BBC only) 
PLOTTERS 


JUKI Hitachi 672 
6100 (Daisy Wheel) £259 (a) Graphics Workstation 


(A3 Plotter) 
NATIONAL PANASONIC Plotmate A4SM 
KX P1080 (80 col) 


£249 (a) 


£369 (a) eee) 


£459 (a) 


£599 (a) 
£450 (a) 
£149 (a) 


PRINTER ACCESSORIES 


We hold a wide range of printer attachments (sheet feeders, tractor feeds etc) 
in stock. Serial, parallel, IEEE and other interfaces also available. Ribbons 
available for all above plotters. Pens with a variety of tips and colours also 
available. Please phone for details and prices. 


Plain Fanfold Paper with extra fine perforation (Clean Edge): 
2000 sheets 9.5” x 11° £13(b) 2000 sheets 14.5” x 11” £18.50(b) 
Labels per 1000s: Single Row 3;” x 1 7/16” £5.25(d) Triple Row 2-7/16" x 1 7/16" £5.00(d) 


MODEMS 


All modems carry a full BT approval 








RT256 3 PORT SWITCHOVER 
SERIAL INTERFACE 

3 input/4 output or 1 input/3 output 
manual channel selection. Input/ 
output baud rates, independently 
selectable 7 bit/8 bit, odd/even/none 
parity. Hardware or software 
handshake. 256K buffer, mains 
powered 





MIRACLE TECHNOLOGY WS Range 


WS4000 V21/23 (Hayes Compatible, 
Intelligent, Auto Dial/Auto Answer)............ £149 (b) 


WS3000 V21/23 Professional As WS4000 
and with BELL standards and battery back up 







PB BUFFER 
Internal buffer for most Epson 








































TOR TIGIMONY tines cccrtciaridans senageadsanencuadsaadaunsen £245 (b) sine Easy to install. Inst. 
WS3000 V22 Professional As WS300 V21/23 PB128 128K 

but with 1200 baud full duplex ................... £450 (a) 

WS3000 V22 bis Professional As V22 and 

2400 David [Ul GUDICK .....<.cncsuncesincssriaceianes £595 (a) 

WS3022 V22 Professional As WS3000 but 

with Only 1200/1200 o..scccccccscsscseeeeeee £350 (a) I.D. CONNECTORS 
WS3024 V22 Professional As WS3000 but Nogt Mester cree eave 
with only 2400/2400 .........0... eee ees £450 (b) 

WS2000 V21/V23 Manual Modem.............. £95 (b) 

DATA Cable for WS series/PC or XT ......... £10 (d) 

DATATALK Comms Package 

* If purchased with any of the above 

FIOGINS © xirsacecerehresteceecncrimanenens seperate *£70 (c) 


D CONNECTORS 


No of Ways 
9 15 25 37 





PACE Nightingale Modem V21/V23 










MALE: 

Ang Pins 120 180 230 350 
Solder 60 85 125 170 
IDC Mie-210 geo -= 
FEMALE: 

St Pin 100 140 210 380 









SOFTY Il 

This low cost intelligent eprom programmer can program 2716, 2516, 
2532, 2732, and with an adaptor, 2564 and 2764. Displays 512 byte 
page on TV - has a serial and par- Ang Pins 160 210 275 440 
allel 1/O routines. Can be used as an emulator, cassette interface. Solder 90 130 195 290 
deh ee aoe a hob andy Ales Gato eed ee i IDC 195 325 375 — 
§ StHood 90 95 100 120 
Screw 130 150 175 — 

Lock: 









PLEASE TELEPHONE FOR 
CURRENT PRICES are, EXTOOL en £7.50 
28-pin £9.10 40-pin£12:10 





10 














Serial Cable switchable at both ends 
allowing pin options to be re-routed or 
linked at either end — making it possible 
to produce almost any cable 
configuration on site. 
Available as M/M or M/F 





DISC DRIVES 
5.25” Single Drives 40/50 switchable: 
TSAO AOC CAO ccs dcctie cite vsudenvgieas cea ierenees aan Ate at xawn ture asenen duals eetanmegeuneannaetade ..... £114 (b) 
PS400 400K/640K with integral mains power SUPDIY «0.0... eee eeeeeeteeeeeteteneeentieeeees £129 (b) 
5.25” Dual Drives 40/80 switchable: 
FI BOO BOOK SOO save vcc.iscidia ict ticcvoshptenat preveatiosnesetaocietens tacdvatteatiny ealny'cedas dtuasesisendianialiscdivenees £199 (a) 
PD800 800K/1280K with integral Mains power SUPPLY... ce eeeeeeeeeeeeeeeeesestnaeeeees £229 (a) 
PD800P 800K/1280K with integral mains power supply and monitor stand..................... £249 (a) 
3.5” 80T DS Drives: 
TS 95 VSI BOO I rss ew erctsersrcrratpsaen ntorniee iduotinapsatemengoensennet ah Gunseaounemeestromcaccesatoematers £99 (b) 
PS351 Single 400K/640K with integral mains power SUPPIY «0.00... ee cece eeeeeeeeeeeetees £119 (b) 
WG 52 Dla) BOOK TBO sis scen ccc ciaeecueidt nw rnnponu iiniscccineiinieua i aiemieanaiabuals £170 (b) 
PD352 Dual 800K/1280K with integral mains power SUPDIY .......... cece eeeteeeetteeeeetteeeees £187 (b) 
PD853 Combo Dual.5.25'/3.5" Give With 0. SB. deacisisainssedravcinredenamiecsercuhariniteoreasenisdisies £229 (a) 
3M FLOPPY DISCS 
Industry Standard floppy discs with a lifetime guarantee. Discs in packs of 10 
5%" Discs 32" Discs 
40 TSS DD £10.00 (d) 40T DS DD £12.00 (d) 80 T SS DD £20.00 (d) 
80 T SS DD £14.50 (d) 80 T DS DD £15.50 (d) 80 T DS DD £25.00 (d) 


FLOPPICLENE DRIVEHEAD CLEANING KIT 





FLOPPICLENE Disc Head Cleaning Kit with 28 disposable cleaning discs 
ensures continued optimum performance of the drives. 51%" £12.50 (d) 


32" £14.00 (d) 


DRIVE ACCESSORIES 


Single Disc Cable £6 (d) 
10 Disc Library Case £1.80 (d) 
50 « 5%" Disc Lockable Box £9.00 (c) 


Dual Disc Cable £8.50 (d) 
30 ~ 512" Disc Storage Box £6 (c) 
100 x 512" Disc Lockable Box £13 (c) 





MONITORS 

RGB 14” MONOCHROME 
1431 Std RES oo. eens £179 (a) TAXAN 12” HI-RES 
1451 M6G ROS 2. ccsiccicrevenvereciaveussnsinseas £225 (a) KX1201G green SCreeN............. eee £90 ( 
NAAT FEROS. occccsccescisvoseverstseorevesanvensss £365 (a) KX1203A amber SCreen.................066 £95 ( 
MICROVITEC 14” RGB/PAL/Audio PHILIPS 12” HI-RES 
TASTAP Std RES sci ccctivincteiateascmayocensi £199 (a) BM7502 green SCreen ............eceee ETS ( 
1451AP Std RES 00... eee £259 (a) BM7522 amber Screen................::: £79 ( 
All above monitors available in plastic or 8501 RGB Std ReS..............c cece £139 ( 
metal case. 

ACCESSORIES 
TAXAN SUPERVISION I! Microvitec Swivel BaSe ............ ee £20 ( 
12” — Hi Res with amber/green options. Taxan Mono Swivel Base with 
IBM COMPANDIG Ss ccrcassssancciascecsetagsuccneies £279 (a) CIOG ne sssanteosmissieiwniaton nerianeteuncatyapeeeices £22 ( 
Taxan Supervision II... £319 (a) Philips Swivel BaSe..................::::ceee £14 ( 

BBC RGB Cable .............ccceceeeeteeees Lo( 
MITSUBISHI WICTOVNEG ai iiiicancimaiorwecnani £3.50 ( 
XC 1404 14” Med Res RGB, IBM & BBC Taxan £5 (d).............. Monochrome £3.50 ( 
COTA Ss cn sicurecisacninin mmadertuaneneanincs £219 (a) TOUCHIOG = 504: cacccssstcsacechasetsenenavecss £239 ( 


UVERASERS 


UV1T Eraser with built-in timer and mains indicator. 


Built-in safety interlock to avoid accidental exposure 
to the harmful UV rays. 


Itcan handle up to Seproms at atime with an average 


erasing time of about 20 mins. £59 + £2 p&p. 


UV1 as above but without the timer. £47 + £2 p&p. 
For Industrial Users, we offer UV140 & UV141 era- 
sers with handling capacity of 14 eproms. UV141 has 
a built in timer. Both offer full built in safety features 
UV140 £69, UV141 £85, p&p £2.50. 


Serial Test Cable 















£24.75 (d) 











Serial Mini Patch Box 


Allows an easy method to 
reconfigure pin functions 
without rewiring the cable 
assay. Jumpers can be used 
and reused. 





EXT SERIAL/PARALLEL 
CONVERTERS 
Mains powered converters 
Serial to Parallel .....0....0ccccccccceeccceeeceeeceeueeees £4é 
Parallel to Serial ........0....cccccecccceeeeececeeevceeeees £4 
Bidirectional Converter.............0.ccccccceeee genes £105 





Serial Mini Test 
Monitors RS232C and CCITT 
V24 Transmissions, 
indicating status with dual 
colour LEDs on 7 most 
significant lines. Connects in 
Line. £22.50 (d 











£22 (d) 





















8 pin Video Connector 


TECHNOLINE VIEWDATA SYSTEM. TEL: 01-450 9764 

























































































































EDGE AMPHENOL RIBBON CABLE 
CONNECTORS aavmnecel 
CONNECTORS 36 way plug Centronics 10-way 40p -34-way 1 
01 0156 (solder 500p (IDC) 475p 16-way 60p 40-way 16 
2x 6-way (commodore) — 300p 36 way skt Centronics 20-way 85p 50-way 2 
2 x 10-way 150p - (solder) 550p (IDC) 500p 26-way 120p 64-way 26 
ae He way (vic 20) .— ae 24 way plug IEEE (solder) 
x “Wa — 
2xz3way 2x8) 175 2200 | 7 ay out IEEE (solder 
2x 25: 2 
Bway (spectrum 2000” | $00p (IDC) 500p DIL HEADERS 
2 x 36-way 250p  — PCB Mtg Skt Ang Pin | Solder IDC 
1x 43-way 2600p — — 24 way 700p 36 way 750p 14 pin 40p 100 
: x re way i — 16 pin 50p 110 
x - —_ . 
sae aeeld 400p S00p GENDER CHANGERS : ae 70 | _ 
0 ; = _ 
2x 50-way(S100conn, 600p 25 way D type 24 pin 100p 150 
EURO CONNECTORS MaletoMale e190. | 28 pin La 
Male toFemale......... £10 ?) ? 
DIN 41612 Plug Skt sie ei 
2 x 32 way St Pin 230p 275p emale to Female £10 
2 X 32 way Ang Pin 275p 320p 
3 x 32 way St Pin 260p 300p RS 232 JUMPERS ATTENTION 
3 X 32 way Ang Pin 375p 400p bawar bi All prices in this double | 
IDC SktA + B 400p 24° Single end Male £5.00 | advertisement are subje: 
IDC SktA+C 400p ae Single end Female £5.25 change without notice 
4" F 
For 2 X 32 way please specify 24" hey Hs ios ep ALL PRICES EXCLUDE ' 
spacing (A + B, A + C). 24" Male Female £9.50 Please add carriage 5( 
unless indicated as follo 
MISC CONNS DIL SWITCHES (a) £8 (b) £2.50 (c) £1.56 
21 pin Scart Connector 200p 4-way 90p 6-way 105p £1.00 


200p 8-way 120p 10-way 150p 











Using ‘Prestel’ type protocols. For information 


and orders — 24 hour service, 7 days a week 


PRACTICAL ELECTRONICS AUGUST 1989 














































COMPUTER COMPONENTS 

















































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































1 SERIES 74279 74.S273 1.28 4076 0.65 
. oy 74283 105 | 74\S279 0.70 4077 0.25 LINEA R ICs 
: 74742 3.20 74LS280 1.90 4078 0.25 i LM71 F TBA231 ; 
\ 0.30 74290 0.90 74LS283 0.80 4081 0.24 SNTSOG: ao LM 7 “er TBA800 0.80 CPUs EPROMs 75154 1.20 KEYBOARD 
‘ +36 AM7310DC 12.00 7 1.00 mre are face sete 
‘ oso 74293 0.90 | 7418290 0.80 4082 0.25 f AN103 200 | LM723 0.60 | TBA810 0.90 TMS4500 14.00 et ape DECODERS 
74298 1.80 | 741S292 14.00 4085 0.60 | AN-1-5050 1.00 LM725CN 3.00 TBA20 0.80 oe 1050 F Tms9901 5.00 fF o716.45 4.50 75161 6.50 
0.36 74351 2.00 | 74LS293 0.80 4086 0.75 § AY-3-1350 5.00 LM733 0.65 TBAB20M — (0.75 pene “50 fF tms9902 5.00 } 5737.45 4.50 
re 74365A ogo | 7418295 1.40 4089 120 [| ay.3-8910 «490 | LM741 0.22 | TBA920 = 2.00 65C02-2MHz TMS9914 14.00 | 976405 4.00 ca Hoes 740922 5.00 
. 74366A 0.80 } 7418297 14.00 4093 0.35 AY-3-8912 5,00 LM7747 0.70 TBA950 2.25 27064 4.50 75182 0.90 8.00 
0.40 Ff 74367A 0.80 | 741S298 ‘1.00 4094 0.90 | CA3019A ~=—-'1.00 -FsLzas 0.30 § C9109 5.00 | 6502A 6.50 - 74C923 
se 74376 1.60 | 7418299 2.20 4095 0.95 ff CA3020 3.50 J LM1011 4.80 J TCA270 350 f 85028 oe fee = z7C286. 5.50 7589 ve 
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74393 120 | 741S322A 3.90 4097 2.70 | ca3z04s 0.70 «fF Lmi801 ~—- 3.00 «J «TOAIOIO §=— 2.28 (8802 3.50 9 Z60CTC = 2.50 . ENERATORS 
: ae 74490 1.40 | 741S323 3.00 4098 0.75 — CA3059 3.25 LM1830 2.50 TDA1024 1.10. = 8809 650 § za0AcTC 2.75 | 27513 18.00 75450 0.80 HRS 
2 ite 74L$324 3.20 4099 0.99 — CA3060 3.50 | LM1871 3.00 TDA1170S 3.00 § 6809E 10.00 J zsoDarT 6.50 J 27C128 = 5.50 Bf 7585) 
¥ vid 74LS348 2.00 4501 036 | casce0e 0.70 | imis72 300 | TDATI70N 3.00 | 68809 10.00 | zeoapaRT 7.00 | 27286 age ee MC14411 7.50 
a 74L$352 1.20 4502 055 f cases 150 | Lmiese 6.00 | TDA2002 3.25 J G8B0SE — 12.00 tis COMB116 6.50 
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ea 74L$356 —2.10 4504 0.95 § CA3089E 250 | LM2917 3.00 TDA2004 2.40 8035 3.50 ae 
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74L$365 0.50 4507 0.35 f CA3130T 1.30 | LM3909 1.40 TDA2593 5.00 : 
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7 0.32 J 74LS00 0.24 | 7419373 0.70 4512 055 f CA3160E 150 | LM3916 3.40 § TDA7000 350 § 9086 22.00 —— =e is pir M6402 
043 74LS01 0.24 | 7419374 0.70 4513 1.50 | casieie 2.00 | LM13600 1.50 | TEAt002 7.00 | 80875 = £120 fF ZB0BCTC— 5.00 ied = 
p 0.30 f 74LS02 0.24 | 7418375 0.75 PE 4514 1.10 | ca3zi62e 6.00 | M51513L 230  TLoICP 0.40 § 8087-8 He eer Re = biped 
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i 0.30 J 741805 0.24 | 7419379 1.30 4517 220 | ca3280G 3.00 | MC1310P ~='1.50. J TLO71 0.40 f 8748 10.00 sdaepeed ape 6MHz 3.75 
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a ped 7aS11 024] 7as33 10 110 No off 4521 1.15 ff DACOs08 3.00 | MC1496 = 0.70 TLOB2 055 gf V20-8 12. Serie bape VISION 
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g : 74LS24 0.50 J 74LS540 1.00 4532 0.65 ICM7556 1.40 ML922 4.00 UCN5801A 6.00 2114-3 1.00 aii DISC 225 
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; np 74LS37 0.24 | 74LS9628 2.25 4551 1.00 LF353 0.90 NE564 4.00 ULN2803 1.80 6116LP-15 6.50 arene. 108 
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nic 74LS40 0.24 74LS640 2.00 4555 0.36 LF356N 1.10 NE566 1.50 UPC575 2.75 6810 2.50 6843 pero pee 
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« spe 74LS48 0.90 | 74.5642 2.50 J4ALS00 4560 1.40 LM10CLH 4.50 NE571 3.00 UPC1185H 5.00 ADC0808 —- 10.00 FD1791 5 oOMite 180 
a pes 74LS49 1.00 | 74LS642-1 3.00 74ALS02 0.45 | 4566 1.40 LM301A 0.30 NE592 0.90 XR210 4.00 AD561J —20.00 FD1793 S068MH2 1.78 
a ion 74851 0.24 | 74.9643 2.50 74ALS04 050 | 4568 2.40 LM307 0.45 NE5532P 1.50 XR2206 4.50 AM25S10 _—-3.50 FD1797 8.00MHz 146 
a ah oe 0.24 | 74LS643-1 3.00 741808 0.50 | 4569 1.70 ff LM308CN 0.75 | NE5533P «= 1.60. J XR2207 3.75 AM2%LS2521 ible 6.144MHz 1.40 
“ ged pe be 74LS644 3.50 74ALS10 0.45 | 4572 0.45 LM310 2.25 NESS34P = s«a1.20 «| XR2211 5.75 3.50 WD1691 SOOMHs 180 
* 210 TAL ctaa ed 74LS645 2.00 74ALS20 0.45 | 4583 0.90 LM311 0.60 NE5534AP ~—- 1.50 XR2216 6.75 AM25LS2538 Ww02143 7 16MHz 175 
- osé 74LS645-1 4.00 74ALS32 0.45 | 4584 0.48 LM318 1.50 OP-07EP 3.50 XR2240 1.20 3.50 WD2793 8 OOMHz 180 
* aie 74LS75 0.45 74LS668 0.90 J4ALS74 0.70 | 4585 0.60 LM319 1.80 PLLO2A 5.00 ZN404 1.00 AM26LS31 1.20 WD2797 876M 175 
P 74LS76A 0.36 | 74.8669 0.90 4724 1.50 LM324 0.45 | RC4136 0.55 9 ZN414 0.80 ; ene 
B2A 0.70 74LS78 0.42 741 8670 170 74ALS138 1.50 aya be zN419P “7 AM26LS32 1.20 10.0CMHz —-'1.75 
b3A 055 : 74ALS139 1.50 : LM334Z 1.15 RC4151 2.00 . AM7910D0C 25.00 10.50MHz 2.50 
3 74LS83A 0.70 74LS682 2.50 J4ALS244 4.00 | 14412 7.50 LM335Z 1.30 RC4195 1.50 ZN423E 1.30 
a 110 7 74.885 0.75 | 74LS683 3.00 14416 3.00 LM336 1.60 | RC4558 0.55 | ZN424E 1.30 aeadey ee CHARACTER a 
A ee Reanpee fo 7aals2as 475 | M4416 _ ee ee ao kwiceh ax jabs 400 | 08304 450 Metals? Wael st 11.00MHz 3.00 
0.80 74LS90 0.48 74ALS573 2.60 ; : : DS3691 4.50 12.00MHz 1.50 
seo 74LS687 3.50 74ALS574 450 | 14490 4.20 LM348 0.60 SN76013N 5.00 | ZN426E8 = 3.00 74S188 1.80 $8830 140 1400NHz 1.78 
te 74LS92 0.35 74LS688 3.50 74ALS580 2.60 14495 4.50 LM358P 0.50 SN76033N 5.00 ZN42¢E8 6.00 74S287 2.25 0S8831 1.50 RO32513UC 1431MH 180 
aes 74LS93 0.54 | 74.S783 145000 6.50 LM377 3.00 | spozseal2 7.00 | ZN4@EB 4.50 74S288 1.90 Ff pnceaso es a seheG be 
paid 74LS95B (0.75 14599 2.00 LM380N-8 1.50 SP8515 750 | ZN429E8 2.25 74S387 228 | cana, Hee RO32513LC ‘cee oe 
on 74LS96 0.90 22100 3.50 LM380N 1.50 TA7120 1.20 ZN447E 9.00 82823 1.50 DS8836 1.50 16.00MHz 2.00 
casolCU 22101 7.00 LM383 3.25 | TA7130 140 | ZN4481 7.50 828123 190 oceans ase as. Fe 
eo rt ae 22102 7.00 LM384 2.20 | A7204 150 | ZN449E 3.00 82S129 oe eee ren 
. . A TELETEXT 18.00MHz 1.50 
110 | 7418112 0.45 40014 0.48 ff} LM386N-1 1.00 J Ta7205 = 0.90 | 2NAS0E_ 7.50 MC1488 (0.60 18.432MHz 1.50 
170 | 7418113 0.45 4006 0.70 | 40085 1.20 9 LM387 2.70 f 1A7222 iso | eee Oe MC1489 0.60 DECODER 19.969MHz 1.59 
100 | 74iS114 0.408 74S SERIES 4007 0.25 | 40097 0.36 LM391 1.80 TA7310 150 | ZN1034E = 2.00 Hees sas Scie. ie 
oss | 7418122 0.70 | 74800 0.50 | 4008 0.60 | 40098 0.40 LM392N 1.10 Nao 600 MC3459 4.50 24.000MHz 1.75 
070 | 7418123 0.80 | 74802 0.50 4009 0.45 | 40100 1.50 LM393 0.85 ZNAI34H 23.00 MCS3470 4.75 48.000MHz 1.75 
0.80 | 7418125 050 | 74804 0.50 | 4010 0.60 | 40101 1.25 LM394CH 4.00 NAGE MC3480 —-8.50 116MHz 2.50 
0.65 | 7418126 0.50 | 74S05 0.50 f 4011 0.24 J 40102 1.30 LM709 MC3486 2.25 PXO1000 «12.00 
055 | 7418132 0.65 } 74808 0.50 J 4012 0.26 J 40103 ae 8253C-5 MC3487 2.28 
055 | 7418133 055 | 74S10 0.50 J 4013 0.36 7 40104 1.20 B255AC-5 3.20 MC4024 5.50 
0.75 | 7418136 045 | 74S11 0.75 | 4014 0.60 rte hy 8256 18.00 MC4044 = 5.50 Please note: 
0.70 74.138 0.55 ven - ae O70 F510? re 8257C-5 54.00 bonded —, oe All prices are subject to 
0.90 4LS139 0.55 : 14411 7.50 ; 
oso -| 7418145 oa 74530 0.80 4017 oss | -40108 3.20 8259C-5 4.00 UPGRADES cians 44a change without notice. 
130 | 74L8147 1.75 | 74832 0.60 | 4018 0.60 | 40109 go 8275 75107 0.90 Only current prime grade 
270 | 74LS148 1.40 74837 0.60 4019 0.60 | 40110 2.25 1A FIXED VOLTAGE PLASTIC TP220 8279C-5 4.80 75108 0.90 components stocked. 
1.10 ] 74LS151 0.65 74$38 0.60 | 4020 0.80 | 40114 2.25 ae a pa 400 75109 1.20 ; 
1.70 74L$152 2.00 74S40 0.50 4021 0.60 | 40107 2.80 8087-5 75110 0.90 We also stock a wide 
140 | 7418153 0.65 74$51 0.60 | 4022 0.70 | 40163 1.00 5V 7805 0.45 si on 8284 4.60 | 3087-8 75112 1.60 range of: Transistors, 
1.75 gai ; - _ - - ~ se ip . oe ee oi — . se le » 3 1.20 Diodes, Triacs Plastic, 
ge 74LS156 0.65 74S85 5.50 4025 0.24 40175 1.00 12V 7812 0.45 7912 0.50 8755A 80287-8 75115 pes Bridge Rectifiers, 
1.40 74LS157 0.50 74586 1.00 me poe pat = ae ba pe be a 8087-10 75121 140 Thyristors and Zenors. 
0.80 | 74LS158 0.65 748112 0.90 7 40 , ; ’ 75122 1.40 i 
os | 74S160A 065 | 748113 120 1 4028 0.60 | 40194 1.06 24V 7824 0.50 7924 0.50 Please phone for details. 
225 | 74LS161A 0.75 748114 1.20 4029 0.75 | 40244 1.50 
1.10 | 74LS162A 0.75 748124 3.00 4030 0.35 pa eed 1A FIXED VOLTAGE PLASTIC TO92 OTHERS LEDs OPTO-ELECTRONICS 
0.80 | 74LS163A = 0.75 ples hee ps pe 40373 186 SV 78L05 0.30 5V 79L05 045 | Bpx25 0.128" BPX25 
1.10 | 74\S164 0.75 | 748133 - 40374 180 6V 78L06 0.30 12V79L12 0.50 | Bpw21 BPX34 
1.10 J 74.S1654 10 748138 1.80 8038 hoi pees ps BV 78108 0.30 15V 79115 050 | oRPi2 REDTIL2090 0.128 ty 299 BPW21 
1.20 | 74LS166A = 1.50 | 748139 Lee] pes a 12V78L12 0.30 TIL211 0.16 cay21 
748140 1.00 | 4034 2.50 | 80C97 0.75 ORP6O oie) TIL222 
1.10 | 74.8168 1.30 15V 7815 0.30 ORP61 YELTIL212 0.20 FND357 
1.40 | 74LS169 1.00 748151 1.50 4035 0.70 | 80C98 0.75 TIL226 
t. louees ta sais ee ener os SFH205 Rect LEDs MAN74.DL704 
OTHER REGULATORS TIL31B (R/GY) 0.30 MAN71 DL707 
2. oe Ae pedis oo bed TIL81 CXQ (Bi colour) MAN4640 
4.20 74LS174 0.75 74S 158 2.00 4038 1.00 COUNTERS 
140 | 7418175 0.75 74S163 3.00 | 4040 0.60 MANE610 
10 LED 74C925 MAN89100.8" 
1.10 7 74LS181 2.00 Lesh pea) Mesek spa Bar Graph 74C926 NSB5881 
1.05 74LS183 1.90 748174 3.00 4042 0.50 FIXED REGULATORS Red 225 74928 ORP12 
100 | 7418190 0.75 74S175 3.20 | 4043 0.60 LM309K 1A 5V 1.40 al ean siete 
150 | 74LS191 0.75 748188 1.80 | 4044 0.60 LM323K 3A 5V 3.50 id 
150 | 7418192 0.80 748189 1.80 | 4045 1.00 L78HOSKC 5A 5V 7.50 FRO MANcci0 | 2 LM3914 Ue 
1.00 | 74LS194A 0.75 74194 3.00 | 4046 0.60 DISPL Nsp5e81 _—5.70 LM3915 es 
3.40 | 74LS195A 0.75 745195 3.00 4047 0.60 FND357 1.00 ff 111311 6.50 LM3916 riLB1 
1.40 74LS196 0.80 74S196 3.50 4048 0.55 FND500/TIL370 TIL728 1.00 UDN6118 TIL100 
1.80 74L$197 0.80 74S200 4.50 4049 0.36 1.00 TIL7300 1.00 UDN6184 TIL311 
1.80 74L$221 0.90 748201 3.20 4050 0.35 VARIABLE REGULATORS FND507/TIL729 MAN8910 ULN2003 
130 | 7418240 0.80 748225 5.20 | 4051 0.65 LM305AH 2.50 1.00 Tt anso4o 
130 | 7415241 0.80 745240 4.00 | 4052 0.60 LM317T TO-220 1.20 patie O87 0 (Och te > 
1.10 74L$242 0.90 748241 4.00 4053 0.60 LM317K TO3 2.40 MAN71/DL707 DISPLAY ULN2802 TIL111 
115 | 7418243 0.90 74$244 4.00 | 4054 0.80 LM337T 2.25 100 DRIVERS pire ILD74 TIL112 
110 | 7418244 0.70 74S251 2.50 } 4055 0.80 LM350T 4.00 eee MCT26 TIL113 
080 | 7418245 0.90 74S257 2:50 | 4056 0.85 LM723N 0.50 aiiwad. aoe igh MCS2400 1. TIL116 
1.30 74LS247 1.10 748258 2.50 4060 0.70 MAN4640 200 75492 MOC3020 6N137 
1.10 | 74LS248 1.10 74S260 1.00 } 4063 0.85 ILa74 6N139 
748261 3.00 | 4066 0.40 
el, 745283 2.70 | 4067 2.30 LOW PROFILE SOCKETS BY TI WIRE WRAP SOCKETS BY TI 
=a i) 6 | CUS SWITCHING REGULATORS 
1.10 | 74LS253 (0.75 74S287 2.25 | 4068 0.25 c1.7680 a Bpin 9p 18pin 16p 24pin 24p 8pin 5p 18pin 5p 24pin 0p 
1.00 | 74LS256 0.90 748288 2.00 | 4069 0.24 563524 res 14pin 10p 20pin 18p 28pin 26 14pin  35p 20pin 60p 28pin 80p 
1.50 } 74LS2457A 0.70 74S289 2.25 | 4070 0.24 TLaa4 3.00 16pin 11p 22pin 20p 40pin 30p 16pin 40p 22pin 65p 40pin 100p 
265 0.80 § 74LS258A 0.70 74S299 4.50 4071 0.24 . 







74L$259 748373 ‘ TL497 245 


nga ' oo : sae ; | TURNED PIN 18pin  25p 16pin 35p 20pin 450p 28pin 


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PRACTICAL ELECTRONICS AUGUST 1989 11 






















his article describes a new stepping 
motor driver ic M5804 which offers 


higher power and more operation 


modes than the commonly used SAA1027. 
A full practical design is given to allow this 
chip to be used in all modes driven either 
from a computer or a simple pulse generator. 


SIEPrEn MOTORS 





Stepping motors are becoming more and 
more popular as a means of providing 
precise computer controlled movement. 
Their applications in plotters, printers, 
buggies, and scanners are well known, but 
there are many other applications — for 
example, greenhouse vent controls, and 
antenna positioning systems, where 
stepping motors are ideal. In the hobby and 
educational fields low cost stepping motors 
find practically unlimited applications, 
particularly in technology, and cdt projects. 

In order to drive a stepping motor from a 
computer output port, some form of 
interface is needed. The simplest is a set of 
four power transistors (usually high gain 
Darlington types) each connected between 
one output port line and one motor winding 





VDD SUPPLY 


— QUTPUT 
OE ENABLE 


DIRECTION 
GROUND 
GROUND 
STEP INPUT 
HALF-SIEP 


9 | ONE-PHASE 





Fig.1. Simplified circuit of the M5804 stepper motor control ic. 


connection. The computer is then 
programmed to switch the windings on and 
off in the correct sequence to rotate the 
motor. The necessary sequences for the 
various modes of motor drive are shown in 
Table 1. Although the hardware is simple, 


operate in other modes — particularly half- 
step mode, limit its use. One difficulty with 
this ic is that it needs unusually high logic 
levels (logic 1 = 7.5V) on its inputs to 
perform correctly. High logic levels were 
once commonly used in industry because 


STEPPING MOTOR 





TABLE 1 
STEPPING SEQUENCE TABLES 


WAVE-DRIVE SEQUENCE 








12 


DRIVER 


BY MARK STUART 


The new M5804 
becomes a very 
versatile single- 
chip stepper 
interface. 


the programming is relatively difficult, and 
four lines of the output port are needed. 


DEDICATED CHIPS 


A better approach is to use a dedicated 
interface ic which works out the correct 
switching sequence for the motor and has 
four high power outputs which drive the 
motor directly. This approach simplifies the 
computer's job so that only two output port 
lines are required, one sets the direction of 
rotation and the other is programmed to 
change state each time a step is required. 
The most common dedicated ic for this job 
is the SAA1027 which handles up to 
400mA at 12V on each output and provides 
bi-directional full step control. 

In many applications this ic is adequate, 
but its low output capability and inability to 





they provide higher noise immunity than 
normal 5V circuits. To raise 5V levels to 


these higher levels takes additional 
circuitry. 
Many stepping motor applications 


require higher performance drive circuits 
which are capable of half-step operation as 
well as the usual two-phase (full step) mode 
and can provide higher output power. Even 
simple applications benefit from half-step 
drive which gives smoother running as well 
as halving the step angle doubling the 
number of steps per revolution). 

The M5804 ic introduced in this article is 
able to handle up to 35V and 1.25A per 
phase (SOV 1.5A peak) and has three motor 
drive modes: half-step, one phase, and the 
standard two-phase. The inputs to the ic are 
compatible with standard cmos, pmos, and 
nmos circuits and with the addition of 


Fig.2. Output transistor detail 


PRACTICAL ELECTRONICS AUGUST 1989 














[0561530] 





Fig.3. Input circuit details 


appropriate pull-up resistors, ttl and Isttl. 
This means that the ic can be connected 
directly to any computer parallel output port 
and drive a wide range of motors directly. 
Another excellent feature of this ic is 
internal thermal protection circuitry that 
disables all outputs when the chip 
temperature exceeds approximately 165° 
and re-enables them at 145°. 


FUNDAMENTALS 


A simplified circuit of the ic is shown in 
Fig.1. Four output transistors drive the 
motor windings. Each transistor is actually 
made up as shown in Fig.2, consisting of a 
standard power Darlington pair with a 
reverse connected parallel diode and 
another diode linked to a separate pin to be 
connected to the positive motor supply. The 
first diode clamps any negative voltage 
swings and so prevents the base-emitter 
junction of the output transistor from 
becoming forward biased. Without this, 
energy from the output can very easily be 
coupled to the input drive circuits — with 
dire consequences. The second diode 
provides an alternative path for the 
inductive motor winding current to flow as 
it decays when the transistor is turned off. 
This is an identical function to the familiar 
connection of a diode across a relay coil, it 
prevents high voltage spikes from breaking 
down the collector-base junction. The two 
diodes are sometimes called "ground 
clamp" and "flyback" diodes respectively. 

The input circuits are the same as 
standard cmos logic as shown in Fig.3. 
These have the usual series protection 
resistor and shunt clamping diodes. 





The supply voltage to the logic section of 
the board can be separate from the motor 
drive supply and must not exceed 7V. As 
only 30mA (maximum) is drawn by the 
logic circuits it is likely that most computer 
systems can be tapped for the necessary 
current from their 5V rails. Alternatively a 
simple zener diode stabiliser can be run 
from the motor drive supply as shown in 
Fig.4. 





A circuit of the ic connected to a motor is 
shown in Fig.5. Most standard unipolar 
stepping motors, such as the MD200 and 
MD35, have a pair of centre tapped 
windings. One winding connects to pins 1, 
2 and 3, while the other connects to 6, 7 and 
8. It does not matter which winding 
connects to which three pins, and provided 
the centre taps are connected correctly the 
two ends of each winding can be connected 
either way round. To make things simple, 
Fig.6 gives the lead colours for the popular 
MD200 and MD35 motors. 


SERIES RESISTANCE 


In many applications it is adequate to 
connect the motor supply directly to the 
winding centre taps, and operate the motor 
at, or even below its rated voltage. This 
arrangement gives adequate performance 
for many applications but does not extract 
anywhere near the full potential from the 
motors. When higher acceleration and 
speed are required it is possible to make 
substantial improvements by raising the 





Fig.4. Zener stabilised logic supply. 


MOTOR 
SUPPLY 


560 
470 
330 
180 


PRACTICAL ELECTRONICS AUGUST 1989 





TANTALUM 


SELECT RS FOR 40mA 


MOTOR CONTROL PROJECT: 


Vienelshool\senleltc 








116] YOO suPPLY 
<= QUTPUT 
115 | O€ ENABLE 


DIRECTION 


13 | GROUND 
12] GROUND 























RED 
WHITE A*~ 


BROWN 


BLUE 


WHITE © 


YELLOW 


MD35S - 48 STEPS PER REV. 


% DETERMINE THE INDIVIDUAL WHITE WIRE 
USING THE OHM METER TEST 


RED 
BLACK 


YELLOW 


(0) | 
D 
A C 
BLUE 
WHITE 
ORANGE 


MD200 - 200 STEPS PER REV. 


Fig.6. MD200 and MD35 winding 
colours 


supply voltage and fitting series resistors as 
shown in Fig.5. The higher voltage forces 
the motor current to rise more quickly. If 
left unchecked this would lead to excessive 
current and a very hot motor, but the series 
resistors prevent this, so that the current 
rises much more rapidly, but stops rising 
when it reaches the motor's maximum 
rating. 

Fig.7 shows the current in two cases for 
the MD35 and MD200 motors derived from 
actual oscilloscope measurements on a 
single winding. In the first case the motors 
are powered directly from 12V, and in the 
second case from 25V via a 33 ohm 5 watt 


13 














CURRENT 


rn DIRECT CONNECTION 
25V 33M SERIES RESISTOR 


CURRENT 


*—~12V DIRECT CONNECTION 


25V 33 SERIES RESISTOR 


TIME 


%R1 IS CHOSEN TO GIVE 
THE SAME WINDING 
CURRENT AS IN (qj. 
TYPICALLY 331 FOR 
MD200 AND MD35 
(S WATT RATING) 





Fig.7. Winding current for direct connection and series resistance 


cases. 





series resistor. In both cases the final 
current is the same, but the rate of increase 
is more than doubled. This rapid increase 
gives much higher performance from both 
motors. The penalty for this, of course, is 
wasted power in the series resistance which 
may equal or exceed the power reaching the 
motor. The method is simple though, and 
for small motors the improvement may be 
well worth the extra power. Only two 
resistors are required because the two 
halves of one winding are never on together 
(if they were, the opposing currents would 
cancel and the motor would draw its usual 
current but develop no torque — a condition 
which can occur if the two windings are 
mixed up). 


ELECTRONIC 


CONTROLLERS 





Other more sophisticated methods of 
current control may also be applied to this 
ic. Such methods as pulse control and 
chopper control use electronic circuits to 
allow the ultimate motor performance to be 
achieved while minimising power 
dissippation. These circuits are beyond the 
scope of this article. 


14 


OPERATION 


Fig. 5 shows that the ic has five input 
pins. Pin 15, the output enable pin, turns 
off the output transistors when held at a 
logic 1. Its operation is completely 
independent of the stepping logic. In 
normal operation it would be connected to 
OV. This pin can be used to reduce current 
consumption when the motor is stationary. 
Its main purpose is to allow the ic to be 
used with sophisticated chopper current 
control circuits. 

Pin 14 sets the direction of the step 
sequence and hence the direction of motor 
rotation. Logic 0 produces one direction 
and logic 1 the other. Note that the actual 
direction of rotation depends on the way the 
motor windings are connected and can be 
changed simply by _ reversing the 
connections to one winding. This is 
sometimes more convenient than altering 
the computer program if the motor is found 
to rotate the wrong way. 

Pins 9 and 10 are used to select the 
stepping mode. Table 2 is a truth table 
showing the circuit logic. Normally the 
levels on these pins will be fixed for each 
application to give full-step or one-phase 


drive. When both are held at a logic 1 (Step 
Inhibit) step pulses (pin 11) are ignored. 
This feature is useful in some situations 
where two motors are being driven at the 
same speed but need to be stopped and 
started independently. 

Step pulses can be applied to both motor 
drivers together from a single computer 
output line or oscillator and by using the 
step inhibit feature either or both motors 
can be stopped or started simply. In some 
circumstances it is desirable to change the 
stepping mode while in operation. This can 
be done by connecting each of the two pins 
to a computer output line, and setting the 
logic levels accordingly. Note that these 
lines and the direction control line (pin 14) 
must only change state when the step input 
(pin 11) is in the low state. This is 
necessary to prevent disruption of the step 
sequence which would result in lost or extra 
steps. It is easy to attend to this when 
driving the ic from a computer, but some 
sort of gating arrangement may be 
necessary when simpler drive methods are 
used. 

Pin 11 is the Step Input pin. The outputs 
will advance one sequence position each 
time this pin changes from a logic | to logic 
0. The minimum pulse width required is 
500ns, there is no maximum limit but it is 
advisable to keep the pulse rise and fall 
times reasonably short (as with all logic 
circuits) to avoid problems caused by 
Output transients being picked up by the 
input circuits. 


Sianolencaelllan es 


The step sequences for all three operating 
modes were shown earlier, in table 1. In 
each case the states (on or off) of the output 
transistor are given. Fig. 8 shows a 
simplified motor with just four steps per 
revolution. Practical motors have multipole 
rotors and stators but the principles are the 
same. Windings are energised by switching 
the four terminals to OV according to the 
sequence in table 1 while the positive 
supply voltage is applied to the winding 
centre taps. For each step the rotor aligns 
with the energised stator poles as shown in 
Figs. 9a, b and c. Unmarked poles are not 
energised. The characteristics of each mode 
are as follows: 





ONE-PHASE (or Wave Drive) 

In this mode just one winding is 
energised at a time and the motor executes 
one full step for each pulse (Fig. 9). The 
current consumption is lower than any other 
mode, and the available torque is 
correspondingly less. Acceleration and 
maximum stepping rate are low. 








TABLE 2 
CONTROL LOGIC TRUTH TABLE 

PIN 9 PIN 10 
TWO-PHASE L L 
ONE-PHASE H L 
HALF-STEP L H 
STEP-INHIBIT H H 


PRACTICAL ELECTRONICS AUGUST 1989 











MAGNETISED 


a 7 ROTOR 


.e) 
N 


a 


Fig.8. Diagram of simple 90° per step motor showing relationship of 
coil terminals to poles. 












. aQe 
| 


LI 
4] Ee) 
j 


LJ 
ara Ces 
| 


WN 
(@) 





STEPPING MOTOR DRIVER 





x 
= a = 


5 
7 ay = 





TWO-PHASE (or Full Step) 

As the name suggests, in this mode the 
windings are energised in pairs so that the 
rotor aligns between the energised pair of 
poles (Fig. 9). Since two poles are 
energised at a time, the torque and hence 
the acceleration and maximum stepping rate 
are higher, and the current consumption is 
double that of one-phase drive. The motor 
executes one step per pulse. 


HALF-STEP | 

By alternating between the above 
methods the rotor can be moved to 
alternately align with the poles and between 
them (Fig. 9). This doubles the number of 
rotor positions so that the motor now 
executes one half step per pulse. This mode 
is very popular because it gives finer 
resolution (96 steps with a 48 step motor 
and 400 steps with a 200 step motor). It 
also gives much smoother running and 
freedom from resonance effects which can 
cause unstable running under certain speed 
and load conditions in the other two modes. 
The current consumption changes between 
alternate steps and averages three-quarters 
of the full-step mode. 


_N] [s_o N} [S— 


val 








S 
, Fl cam 


vail 


q 
a= 


> 





Fig.9. (a) Wave drive-one phase, (b) Full step-two phase, (c) Half step mode. 


PRACTICAL ELECTRONICS AUGUST 1989 


15 





MOTOR 
CONNECTIONS 


[0161539 


Fig.10. 
Component layout 
for the printed 
circuit board 


POWER-ON RESET 

When power is first applied to the logic 
section of the ic the states of the outputs are 
automatically set to those shown as step 1 
in the tables. If a separate motor power 
supply is used this can be turned on and off 
freely without affecting the logic states. 


~ CONSTRUCTION. - 


A single small pcb design is all that is 
required for this ic as it requires few other 
components. Fig. 10 shows the component 
layout diagram. The ic may require 
heatsinking in some applications, and this 
can be achieved by soldering copper 
"wings" to pins 4, 5, 12 and 13. I have 
operated all of Magenta's standard motors 
(drawing up to 1A total at 12V) without 
heatsinks of any kind, and the ic has stayed 
quite cool. A single capacitor on the board 
is provided to decouple the logic supply. 

On the input side of the board, a row of 
eight 0.1 in pins are provided for 
connection of the logic power supply and 
control inputs. Next to these pins, a row of 
holes are provided so that any of the inputs 
can be linked either to supply or ground for 
the particular application. 

The output side of the board has a row of 
6 pins, four of which connect to the output 
transistor collectors, with the other two 
being the connections to the two pairs of 
flyback diodes. Provision is made on this 
side of the board for two resistors to be 
fitted if series resistance operation is 
required. In most cases the necessary 
resistor power rating makes it preferable to 
mount the resistors away from the ic, 
connected to the board with flexible wire 
links. 


TESTING 


When completed, the board can be tested 
by connecting four leds (with series 
resistors) between the four output pins and 
the logic supply. The functions of the 








16 





+ LOGIC 


OUTPUT ENABLE 
DIRECTION 

GND 

GND 

SIEP 

HALF-STEP 
ONE-PHASE 


LINKING 


CO] WMO) Nees 


10uF miniature radial 
electrolytic or 
tantalum 35V 
IC] M5804 (Magenta 
Electronics) 
6-way and 8-way in line 
0.1 in pin headers 


Connectors 


Printed circuit 
board Magenta Ref. 1124 

A full kit of parts (including the pcb) is 
available from Magenta for £7.94 + £1 
p&p. A special offer pack including this 
kit and an MD35 stepping motor is also 
offered for £14.99 + £1 p&p — A saving 
of £5.65. Contact: Magenta Electronics 
Ltd, 135 Hunter St., Burton on Trent, 
Staffs, DE14 2ST. Tel: 0283 65435. 


circuit can then be checked one by one by 
linking the appropriate input pins to ground 
or supply. Note that the logic supply should 
be between 4.5V and 5.5V (max 7V) and 
that the circuit will need 30mA plus the led 
current. As the inputs are cmos, they must 
not be left floating in any circumstances. 


| == PROGRAMMING 


Computer programming to drive the ic 
can be very simple indeed as it is a matter 
of writing numbers to the computer output 
port. The simplest program can be written 





ED - LINES 


OUT-SMARTING PIRATES 


ou'll probably have read the section on 
ve Cards in the Home Automation 
feature of May 89. I've now learned of 
another way in which they may make their impact 


felt, as a means to beat satellite pay-tv pirates. 
Currently, French and US tv companies lose 












AREA 





in basic and just consists of a timing loop 
and Two instructions to write to the output 
port. The time delay must be long enough 
to give a stepping rate that the motor can 
follow. This is best determined by trial and 
error and depends on the load and motor 
inertia. A good idea is to start at a slow 
rate, such as 50 steps per second, and 
gradually decrease the time delay until the 
highest practical stepping rate is achieved. 
There is a stepping rate (called the pull-in 
rate) above which the motor will not start 
from a standstill. It is possible however to 
accelerate the motor gradually to higher 
speeds by smoothly increasing the stepping 
rate while it is running. The programming 
for this is more complicated, but very 
interesting, especially as the motor also 
must also be decelerated gradually. For 
many applications it is better to take the soft 
option and stick to constant but lower speed 
running. 


MORE MOTORS 


Magenta have a range of stepping motors 
in stock, all of which can be driven by this 
interface. 

Two types are featured in this article: 

MD 200:200 steps per revolution £16.80 
inc. vat 

MD 35:48 steps per revolution £12.70 
inc. vat 

The interface will drive any other motor 
provided its ratings are not exceeded, and 
that the motor has 4-phase unipolar type 
windings. 











about 30% of their potential pay-as-you-view 
income because of pirates selling illegal decoding 
equipment which enables viewers to receive 
encoded or scrambled signals. Sky TV, which 
intends to introduce pay tv channels later this 
year, will issue smart cards to subscribing 
viewers. They are the thickness of an ordinary 
credit card and have a built-in microprocessor. 
Inserting them into the set-top decoding boxes 
will unlock the unscrambling equipment allowing 
normal viewing. The smart card microprocessor 
will allow Sky to cut off any viewer who has not 
paid the monthly subscription. 


PRACTICAL ELECTRONICS AUGUST 1989 














HIGH GRADE 





COMPONENT PARCELS 


COMPONENT 
PACKS 





This month we have a delicious selection of top grade component packs for you. 
They all contain brand new components of the very highest quality — 
experiment, circuit design and development, or education. All the packs are £1 
(+ VAT) each, but if you order five packs you can select another pack FREE. 


ideal for 


Order ten packs and you can have three extra packs FREE. 


FOR THE EXPERTS - Just look at those ICs! They are all at the very top of their class, made for peak 
performance without compromise. The kind of ICs it’s a delight to design with. 

Of course, there’s no point in buying an expensive IC unless you know exactly how to use it, so each 
comes with its own data sheet, specifications, design ideas and circuits. The nicest thing of all is that any one 
of them could be yours in a few days time if you order right now! 


PASSIVE COMPONENTS 


PACK 1 — 200 RESISTORS. Mostly Y4W carbon 
film. Lots of E12 values with some E96. 

PACK 2 — 100 CAPACITORS. Ceramics, 
metallised film, all types. A fine selection! 
PACK 3 — 30 ELECTROLYTICS. Values to 500pF. 
PACK 4 — 15 LARGE ELECTROLYTICS. 

Values to 5,000pF. 

PACK 5 — 10 TANTALUM CAPACITORS. 
Values to 47pF. 

PACK 6 — 20 HIGH VALUE POLYESTER CAPS. 
Values to 2u9. 

PACK 7 — 15 DIL RESISTOR NETWORKS. 

PACK 8 — 20 CARBON AND CERMET TRACK 
PRESETS. 


OPTO ELECTRONICS & DISPLAYS 


PACK 11 — 105mm LEDs: 4 red, 2 yellow, 
9 orange, 2 green. 

PACK 12 — 10 3mm LEDs: 4 red, 2 yellow, 
2 orange, 2 green. 

PACK 13 — 2 CQY89A high power infra-red 
emitters. 


PACK 14 —2 HIGH POWER SENSORS. 

Matched to emitters in PACK 13. 

PACK 15 —2 FND10 0.1” miniature 7-segment CC 
LED displays. 

PACK 17 — 20 NEON BULBS (use 100k series 
resistor for mains). 

PACK 18 — 2 INFRA-RED COMPONENTS. 

Emitter and phototransistor. 

PACK 19 — 3 FLASHING LEDs. 

A built-in IC makes the LED flash. 

PACK 21 — 1 SLOTTED INFRA-RED OPTO SWITCH. 
PACK 23 — 10 RECTANGULAR GREEN LEDs. 

For bar graph, etc. 


SEMICONDUCTORS 


PACK 26 — 3 TAG136D MAINS TRIACS (400V, 4A). 
PACK 27 — 30 IN4000 SERIES RECTIFIERS. 

PACK 28 — 30 MIXED SEMICONDUCTORS. 
Transistors, diodes, SCRs, ICs, FETs, etc. 

PACK 29 — 90 ASSORTED ICs. 

CMOS, TTL, linear, memory, all sorts. 

PACK 30 — 20 TRANSISTORS. 

High grade general purpose NPN. 


PACK 31 — 1 CF 585 CALCULATOR IC. With data. 


MISCELLANEOUS 


PACK 36 — 4 12V BUZZERS. 

PACK 37 — 3 PANEL NEON LAMPS. 

PACK 39 — 5 ‘BEEHIVE’ TRIM CAPS. 

PACK 40 — 3 VDRs. Mains transient suppressors 
— just wire between L and N of plus. 

PACK 42 — 12 PP3 BATTERY CONNECTORS. 
PACK 43 — 100 MYSTERY PACK. 

At least 100 top grade components. 

PACK 44 —1 MINI BIO-FEEDBACK KIT. 

With PCB, components and instructions. 
PACK 45 —1 MINI DREAM MACHINE KIT. 
With PCB, components and instructions. 


EXTRA PACKS 


PACK 50 — 12 BC212 TRANSISTORS. 
General purpose PNP. 

PACK 51 — 12 BC213 TRANSISTORS. 
General purpose PNP. 

PACK 52 — 2 PIEZO BUZZERS. 

Use as microphone, speaker or buzzer. 





HI-Fl PRE-AMPLIFIER IC £2.80! + VAT 
The HA12017 is a top grade Hi-Fi pre-amplifier, turning ina THD 
of less than 0.002% over the entire audio bandwidth! The low 
noise, wide dynamic range and excellent power supply ripple 
rejection make this IC the first choice for an audio pre-amplifier 
of formidable specifications. 

Each IC is supplied with its own data sheet giving 
performance figures and graphs, the circuit for a top flight pre- 
amplifier and a PCB foil pattern and component layout. 
SPECIFICATIONS 
THD = 0.002% typ. (f = 20Hz to 20kKHZ, Vout = 10V RMS, RIAA) 
Input noise V, = 0.185uV typ. (IHF-A network, Rg = 43R, RS) 


Supply rejection: 
SVR+ = 56cB typ. 
(f= 100Hz, Ry = 43R) 
SVR— = 45cB typ. 
(f= 100Hz, Rg = 43R) 


POWER AMPLIFIER IC £3.90! + VAT 
As easy to use as an ordinary op-amp, the L165V’s massive +3A 
current handling make it the ideal choice for a minimum 
component Hi-Fi amplifier. 

This IC’s data sheet includes circuits for a basic amplifier, a 
motor controller and a power oscillator. A separate sheet gives 
Circuits and construction details for two high quality audio 
amplifiers, one giving 20W and the other 50W output. All 
information comes free with the IC. PCBs for the amplifiers are 
available separately, if required. 

SPECIFICATIONS ; 
Output current: +3A Frequency range: DC to 200kHz 
Supply voltage: 12V to 35V Input noise: 2uV (10Hz to 10kHz) 
ACCESSORIES 20W Hi-Fi amplifier PCB £1.20 + VAT 

50W Hi-Fi amplifier PCB £1.60 + VAT 


HIGHGRADE 





UHF AMPLIFIER £12.20! + VAT 
The OM335 is a high gain wideband amplifier (IOMHz to 
1.4GHz) for VHF and UHF signals. It can be used as a masthead 
amplifier for better TV reception, a booster for indoor aerials, a 
distribution amplifier, and so on. The only external component 
needed is a decoupling capacitor for the power supply! 

Each amplifier is supplied with a data sheet giving 
specifications, design hints and performance figures. A separate 
leaflet, also supplied with the IC, gives a complete design for a 
TV aerial booster, with layout and construction details. A PCB for 
the amplifier is available separately, if required. 

SPECIFICATIONS 

Frequency range: 10OMHz to 1.4GHz 
Mid-band gain: 26cB at V; = 24V 
ACCESSORIES 

PCB for TV aerial booster 
£1.80 + VAT 

Screening piece 

80p + VAT 


Noise figure: 5.5cB typ. 
Supply voltage: 9V to 26V 





BAR GRAPH DISPLAY £3.60! + VAT 
For visual impact, there's nothing to beat a bar graph display — 
you can see at a glance exactly what’s going on. The LM3915 
needs only ten LEDs and a few resistors to make a moving dot or 
expanding bar display. The logarithmic response means that the 
graph will automatically be scaled in dBs and will cover a wide 
dynamic range — ideal for audio work. 

The data we supply with the IC gives circuits for a peak 
detector, VU meter, vibration meter, light meter, audio power 
meter, and a dozen more project ideas! 

SPECIFICATIONS 

Range: 30dB in 3B steps 

Supply voltage: 3V to 25V 

Outputs: direct LED drive (no series resistors needed). 


A/D CONVERTER £4.80! + VAT 
Built-in clock generator, easy interface to microprocessors, 
outputs suitable for MOS and TTL, differential inputs — the 
ADC0804's got the lot! As a stand alone converter, it needs only 
one external resistor and one small cap. What could be easier? 

The converter comes with its own data sheet, giving full 
specifications, design hints and over 25 circuit ideas! Stocks 
limited on this one I’m afraid, and at this price they'll be gone in 
no time, so reserve yours now. 


SPECIFICATIONS 
Resolution: 8 bits Access time: 135ns 
Supply voltage:5V_ Outputs: MOS and TTL. 


COMMUNICATION THROUGH THE MAINS £6.20! + VAT 
Messages through the mains is the function of the LM1893. 
Although intended for reliable, long distance data 
communication, it can just as easily become a powerful mains 
intercom — the instructions tell you how. Each IC contains a 
transmitter which sends an FSK modulated signal along the 
mains wiring of your house or office. The IC also has a receiver to 
pick up and decode the signals, so two ICs will give you full 
two-way Communication without any wires or cables! 

The instruction leaflet gives detailed design procedures, 
Circuits, and everything you need to know to build a speech or 
digital Communications system. 


SPECIFICATIONS 

Transmission rate: up to 4.8kBaud 

Carrier frequency: selectable 50kKHz to 300kHz 

Power boost: optional x10 power boost with single transistor. 


UK Orders: Please add 80p postage & packing 
and 15% VAT to the total (including postage). 
Europe and Eire: Please add £2.50 carriage 
and insurance. No VAT. 

Outside Europe: Please add £4.50 carriage 
and insurance. No VAT. 


COMP ONENTS LTD UNIT 8, 8 Woburn Road, Eastville, Bristol BS5 6TT. 


PRACTICAL ELECTRONICS AUGUST 1989 


17 








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41256-10 SURFACE MOUNT EX NEW BOARDS ¢4 400m 0.5w thick film resistors (yes four hundred megohms) 4/€1 0960p, D15 £1.50, D25 £2, D37 £2, D50 £3.50 covers SOp ea. 
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18 PRACTICAL ELECTRONICS AUGUST 1989 








igh frequency (hf) radio relies on 
Hz waves being bent through the 

atmosphere for the signal to reach 
the distant end. The demarcation between 
low, high and very high frequency radio is a 
demarcation by frequency as shown in 
Fig. 1, and although hf radio will be 
concentrated upon here, the other forms will 
be touched on for completeness. 


RADIO WAVE 


PROPAGATION 





Radio energy can be visualised as 
rippling away from a point source like water 
rippling away when an object is thrown into 
a pond. The only difference is that radio 
energy ripples away three dimensionally, ie, 
in the shape of a spherical front unless 
deliberately suppressed in the backward and 
sideways directions so as to concentrate the 
energy in the forward direction. 

Therefore the power decreases by the 
square of the distance as given by the 
formula 

P = Total power radiated 


4n 2 


Where P is the power at distance y. 
The wavefront consists of an electrical 
component and magnetic component at 


HF RADIO 












Very low 3-30kHz 


frequency (VLF) 
Low frequency 





























30-300kHz 






















(LF) 

Medium frequency 300-3, 0OOOMHz 
(MF) 

High frequency 3-30MHz 
(HF) 

Very high 30-300MHz 

frequency (VHF) 

Ultra high frequency 300-3000MHz 


(UHF) 





Super high 
frequency (SHF) 


Fig.1 Radio frequency bands 


COMMUNICATIONS FEATURE 


100,000- Standard frequencies 
10,000m and time signals 
10,000-1,000m Broadcast, mobile, 


1,000-100m 


100-10m 





100-10cm 














navigation maritime 





Broadcast, mobile, 
navigation maritime 









Broadcast, mobile, 
maritime aeronautic, amateur 












10-1m Radio navigation, radio 


and TV broadcast 


Meteorological, space 
communication, mobile, 
maritime, aeronautic, 
amateur, radio location and 
navigation, TV broadcast 
















Space and satellite, radio location 
and navigation, mobile 











THE GROUND WAVE 


For horizontally polarised waves the 
electric field is short circuited at the earth's 
surface, therefore this method of propagation 
occurs only with vertical polarisation. The 
wave loses some of its energy to the earth 
and is therefore attenuated. The amount of 
energy lost depends on the terrain. For 


the absence of the sun. The E layer helps 
mf propagation and reflects some hf. 

Sometimes a thin layer of high density 
ionisation appears with the E layer and 
remains through the night. Although it does 
not assist long distance communication, it 
gives unexpectedly good reception. 

Of the two F layers, F2 is the more 
important for reflecting hf radio and it 
persists at night. The height and ionisation 








right angles to each other which is referred 
to as a transverse electro-magnetic (tem) 
wavefront. The plane of the electric field 
determines whether the wave is horizontally 
or vertically polarised, Fig. 2. 

In general, electro-magnetic waves 
travel in straight lines except where the 
earth and atmosphere change the path. 
There are three methods of propagation: 

1. The ground or surface wave 
2. The sky wave 
3. The space wave 


Fig.2. Polarisation 


VERTICAL POLARISATION 


E=ELECTRIC FIELD 
M= MAGNETIC FIELD 


M 


DIRECTION OF 
PROPAGATION 


HORIZONTAL POLARISATION 


DIRECTION OF 
PROPAGATION 





PRACTICAL ELECTRONICS AUGUST 1989 


BY MIKE SANDERS 


The first in a series 
on practical radio 
propagation, from 

aerials to 
atmospherics. 


instance this is greater over rocky land than 
over the open sea. 

Propagation by this means is limited to 
low frequencies 20kHz to 2MHz since 
attenuation increases with frequency. 


THE SKY WAVE 


In the earth's atmosphere, where the 
pressure is lower (100km to 300km up), 
free electrons are produced as a result of 
ionisation by energy from the sun. From 
measurements of electron density the at- 
mosphere has been divided into layers D, E, 
F1 and F2 as in Fig. 3. At night the Fl and 
F2 layers combine into a single layer. 

The D layer depends on the latitude of 
the sun and disappears at night. It reflects 
vif and lf waves but does not affect hf 
much. The E layer also disappears at night 
like the D layer owing to de-ionisation in 








density of the F2 layer vary with the time of 
day, season of year and sunspot cycle. 

HF waves are returned to earth not by 
reflection but refraction, Fig. 4. The wave 
is gradually bent so that it finally emerges 
from the atmosphere and returns to earth. 
The refractive index of the layer reduces 
with increased ionisation and there is a 
maximum usable frequency depending on 
the ionisation, height of the layer and the 
angle of incidence of the wave. Above this 
usable frequency, the wave escapes into 
space since it is not bent sufficiently to 
return to earth. 





Fig.3. lonisation layers 


E LAYER 


D LAYER 


3 





19 








ESCAPED RAYS 


i, — 
oa 


ig7 HIGHER FREQUENCY 
RAYS 


GROUND 
WAVE SKIP 
DISTANCE 


The dead space not served either by the 
ground wave or the sky wave is called the 
skip distance. 


THE SPACE WAVE 


Above 30MHz, the ground component is 
greatly attenuated and refraction in the ionosphere 
does not take place. Therefore propagation is 
direct, or line of sight, between transmitter and 
receiver. However the radio horizon is slightly 
greater than the optical horizon. 

In the troposphere, Fig. 5, the lower part of 
the atmosphere, the temperature and density of 
air decrease with height. Therefore the radio 
waves travel slightly faster in the upper 
atmosphere compared to closer to the earth. 


The results in a curved propagation path and 


an increase in the effective horizon. 


EXOSPHERE 


IONOSPHERE 
THERMOSPHERE 


} MESOSPHERE 


} STRATOSPHERE 


} TROPOSPHERE 





Fig.5. Atmospheric bands 


Communications over distances greater 
than implied above and at frequencies in excess 
of 30MHz can be obtained by a phenomenon 
known as scatter propagation. This is because 
both the troposphere and ionosphere are in a 
continuous state of change. Consequently the 
refractive index of the atmosphere changes, 
scattering radio energy, Fig. 6. 

The useful frequency range for 
troposcatter links is 400MHz to 5GHz and 
distances of 800km have been achieved. 
The penalty of course is that rapid fading is 
possible due to multipath delay and the 
signal strength is lower than that usually 
achieved by a direct line of sight link. 

Ionospheric scattering is also possible as a 
result of changes in ionisation of the E layer. 
The useful frequency range is 30MHz to 
7OMHz over a ground distance of 200km, with 
the same penalties as for a troposcatter link. 


20 


Fig.4. Refraction in the ionosphere 













\ONOSPHERIC 
LAYERS 


TRANSMITTER 





SCATTERING 
VOLUME 


NX 
“NX 
~“ ~N 
vA ROPOSPHERE 


RECEIVER 
0461506 


Fig.6. Troposcatter link 


Tht WORK.OF 
MARCONI 





Guglielmo Marconi was born in Bologna, 
Italy in 1874 and died in Rome in 1937. He 
was a physicist and is accredited with much of 
the early work on radio. His early experiments 
with radio communication succeeded in 
detecting a signal 6km across Salisbury Plains 
and 14km across the Bristol channel. 

He founded a company which was renamed 
the Marconi Wireless and Telegraph Company 
in 1990. In spite of mathematicians who said 
that the curvature of the earth would limit radio 
communications to 322km, Marconi sent a 
signal from Poldhu in Cornwall to St John's in 
Newfoundland in 1901. 

In 1918 he had improved his transmitters 
and receivers sufficiently to send a signal 
from England to Australia. His work also 
extended to the higher frequencies employing 
dish aerials for line of sight communications. 


AERIALS 


If an open circuited length of 
transmission line is considered, Fig. 7, 
forward and reflected waves combine to 
form a standing pattern as shown. The 





energy that is not reflected back at the open 
circuit escapes as radiation. 

However, the radiation from the top wire 
cancels that from the bottom wire and only 
a little energy is radiated. If at the open 
circuited end the wires are parted, Fig. 8a, 
to give a horn shape, more energy is 
allowed to escape. Maximum energy 
radiates when the wires are bent at right 
angles to give what is called a dipole, Fig. 


If the total length of the verticals is 
equal to half a wavelength, the aerial is 
called a half wavelength dipole. The 
horizontal radiation pattern of a vertical 
dipole is a circle, Fig. 9a, and the vertical 
pattern is a figure of eight, Fig. 9b, since the 
dipole radiates in both the forward as well 
as backward direction. 


AERIAL RESONANCE 


Resonant aerials could be described as 
opened out transmission lines such that the 
aerial is a half wavelength or a multiple of a 
half wavelength. 

It was mentioned above that the vertical 
radiation pattern from a half wavelength 
dipole is a figure of eight. The vertical 
patterns for increasing lengths of aerial in 
free space are shown in Fig. 10. As the 


Fig.7. Open circuited transmission line. Fig.8. (a) Horn shape, 
(b) Dipole. Fig.9. (a) Horizontal radiation pattern of vertical dipole. 
(b) Vertical radiation pattern of vertical dipole. 


TO GENERATOR 





ibis tall 


RADIATION 


ay) )) 
(a) 





yo 


Fig.9. 


fe 





[0161509] (b) 






PRACTICAL ELECTRONICS AUGUST 1989 




















Fig.12. 


EAMWIOTH 


VOLTAGE AND 
CURRENT 
DISTRIBUTION 


AERIAL 


Vos Vos 
Fig.11. 


RADIATION 


DIRECT RAY 


Fig.13. 





Fig.10. Pattern for increasing length of dipole. 


Fig.11. The non-resonant aerial. 


Fig.12. Beamwidth. Fig.13. Effect of the Earth. 


length of the aerial is increased the pattern 
builds up more lobes and the larger lobes 
come closer to the aerial. 

Non resonant aerials on the other hand 
can be likened to non resonant transmission 
lines which are correctly terminated and 
therefore do not have standing wave 
patterns. Most of the forward energy is 
radiated and the remainder is dissipated in 
the termination, Fig. 11. Therefore the 
radiation pattern of the non resonant aerial 
is similar to that of the resonant aerial 
except that the former has only half the 
pattern, ie the forward pattern. 


SPNINGANID ES eA aL 


Since practical aerials are designed to 
radiate in the required direction some 





means must be found of assessing their gain 
and beamwidth. 

This is achieved by comparing the 
energy with that radiated by an isotropic 
radiator, ie, a theoretical aerial radiating 
uniformly in all directions. 

The beamwidth can then be defined as 
the angle made by the two half power 
points of the main lobe, Fig. 12. 


EARTH ERECT. 


The earth may be thought of as a 
reflecting surface, Fig. 13, and some rays 
will be bounced off. Therefore the energy 
arriving at a particular point may be made 
up of a direct ray as well as a reflected ray 
and if these are in exact antiphase, no signal 
is picked up by the receiver at that point. 





Fig.14. An earthed dipole. 


Fig.15. Aerial directivity with height. 


PRACTICAL ELECTRONICS AUGUST 1989 





In considering reflected rays it is 
sometimes easier to visualise these as 
coming from a mirror image of the aerial, 
ie, an aerial located below the earth's 
surface. 


LOW FREQUENCY 


AERIALS 





These are restricted to frequencies up to 
300kHz and therefore a vertical radiator is 
sufficient. If the previously described 
dipole of overall half wavelength 1s 
connected to a transmitter or receiver as in 
Fig. 14 so that one end is earthed, it has a 
voltage and current distribution as shown. 

Although the aerial is theoretically 
resonant at a height of a quarter of a 
wavelength, in practice this occurs at a 
height of slightly less than 4/4 (where A = 
wavelength). 

Assuming that the resistance is 
negligible, the impedance of the aerial iS 
capacitive for heights up to A/4 and 
inductive between A/4 and A/2. 

For economic reasons the height of the 
aerial may be limited to A/4. For instance at 
300kHz, this would be 800 feet which iS 
quite an expensive tower. Since the aerial 
is capacitive for this height, it can be tuned 
by a series inductance. 

Capacitance is deliberately added to the 
top of low frequency aerials and is achieved 
by turning the top half into an inverted eB; 
or 'T' shape. The additional capacitance 
produces a uniform current distribution on 
the aerial and also reduces the overall 
capacitance of the aerial making a smaller 
tuning inductor possible. 


MEDIUM FREQUENCY 


AERIALS 





One of the most important applications 
of medium frequency aerials (used between 
300kHz and 3MHz) is for broadcasting in 
the range of 550kHz to 1600kHz. 

Early aerials for broadcasting in the 
1920s were 'T' shaped with a piece of wire 
slung between two masts but insulated from 
the masts. There were many areas of fading 
where the ground wave neutralised the sky 
wave and therefore increasing the radiated 
power did not achieve anything. 

It was left to Ballantine to show that 
there is a maximum height of aerial for 
maximum ground wave radiation. This led 
to the construction of a steel tower which 
acts as an aerial. It is on a ball and socket 
joint and insulated from earth, with stays to 
support the mast. 

Fig. 15 shows the effect of increasing 
the height of the mast. At A5/8 a secondary 
lobe appears and predominates over the 
ground wave. Therefore in practice such 
aerials are limited to around A/2. 


21 





Fig.16. Horizontal polar 


diagrams for two vertical aerials 
EELS Sa So a at aria tected 


HIGH FREQUENCY 


AERIALS 





With frequencies of 3MHz to 30MHz 
the wavelengths are 100m to 10m and the 
aerial becomes small enough to point it in 
the direction of maximum signal. It also 
becomes small enough to place on roof 
tops. 

Dipoles can be stacked together to form 
arrays. When they are placed side by side 
they are called a broadside array; placed 
one behind the other they are an end fire 
array; placed one above the other they are a 
collinear array. 

Fig. 16 shows horizontal polar diagrams 
for two vertical aerials spaced a distance d 
apart and with the current in one aerial 
leading the current in the other aerial by 
angle a. 

If a number of vertical aerials are placed 
the same distance apart, the radiation of the 
main lobes is perpendicular to the line 
formed by the aerials, Fig. 17, when the 
aerial currents are in phase. This is a 
broadside array and used quite a lot in 
practice in point to point working. 

Since radiation is required only in the 
forward direction, the radiation in the 
reverse direction is suppressed by means of 
reflectors. The reflectors are similar to the 
aerials physically but they are not fed with 
power. If these reflectors are placed a 
distance of A/4 behind the aerials the 
forward radiation is reinforced, and the 
backward radiation is cancelled, because of 
the currents induced in the reflectors from 
the main radiators. 

In an end fire array the major lobe of 
radiation is along the axis of the array as 
shown in Fig. 16. In its simplest form a two 
element array will be spaced 4/4 and have a 
current difference of m/2. The width of the 
major lobe decreases as the array increases 
in length, but a broadside array of the same 
length provides a narrower lobe, and is 
often preferred. 


22 





AERIAL RESONANCE 


The aerials described up to now have 
been likened to an open circuited 
transmission line radiating energy. Another 
Class of aerials may be considered, termi- 
nated in its characteristic impedance. One 
example is the rhombic aerial, Fig. 18a. 

It is made of four straight lengths of 
wire suspended from posts and the rhombus 
is parallel to the earth. The lengths may be 
from two to eight wavelengths long and the 
angle between them from 80 degrees to 150 
degrees. The angle 0 in Fig. 18b decreases 
as the lengths of wire increase and is 20 
degrees for wires six wavelengths long. 

For the frequency being transmitted, if 
the lengths of wire and the angle between 
them are chosen correctly, the angle 8 in 
Fig. 18b disappears and one main lobe is 
produced which radiates along the diagonal 
from the feeder. 





Fig.17. 





they may still be in a Straight line but 
connected separately to a receiver as in Fig. 
20. If these can be steered to vary the angle 
8 then the signal to noise ratio is improved 
since the down angle of short wave signals 
varies throughout a twenty-four hour 
period. Such a system is called a multiple 
unit steerable antenna (musa) and helped 
the early days of transatlantic telephony. 


AERIAL RESONANCE 


Ultra high frequency (uhf) aerials (300 — 
3,000MHz) employ small aerials as for 
television reception. These have small 
elements and produce a narrow beam 
depending on the number of directors used 
in the Yagi array of Fig. 21. The main 
element is a dipole and is the only one to be 
excited directly. 

The reflector behind the dipole is longer 
than the dipole in order to reflect all the 


S) 


6 = 80 TO 150 DEGREES 


[0101516] 


Fig.18. 


Fig.17. Broadside arrays. Fig.18. (a) Rhombic aerial, (b) Radiation 


pattern. 





The rhombic aerial is used for both 
transmission and reception and is widely 
used in the hf range for point to point 
working. These aerials have replaced 
broadside arrays to a large extent because 
the input impedance and radiation pattern 
remain fairly constant over a wide range of 
frequencies. 

A rhombic aerial also produces minor 
lobes and about half the power is dissipated 
in the termination. These problems are 


Overcome by using two or more rhombics 
in parallel either on top of each other or side 
by side depending on the radiation pattern 
required. 

The aerials may also be connected in 
series as shown in Fig. 19. Alternatively 





Fig.19. Series connected 
rhombics. 

Fig.20. Multiple unit 
steerable antenna. 


backward energy forward. The directors in 
front of the dipole are shorter than the 
dipole and assist beam shaping. 

The object of all radio communication 
systems is to transmit the desired bandwidth 
and detect it at the receiver in spite of the 
noise in the atmosphere and thermal noise 
in the circuits. This means in general that 
the signal has to be above the noise level 
and merely increasing the receiver 
Sensitivity will not improve signal 
detection. Therefore the transmitter output 
must be increased. 

The stages of a radio receiver may be 
summarised as in the block diagram of Fig. 
22 but before we examine the techniques of 
each stage, some revision of circuit theory 





Fig.20. 


RECEIVER 


PRACTICAL ELECTRONICS AUGUST 1989 











DIPOLE 
> DEFLECTORS 


RADIO 
FREQUENCY 


AMPLIFIER 


““ REFLECTOR 


INTERMEDIATE 
FREQUENCY 
AMPLIFIER 


OSCILLATOR 








Fig.21. (left) UHF aerial. Fig.22. (right) Radio receiver block diagram. 


would be useful. For instance thermal noise 
mentioned above is present in every circuit. 
Also tuned circuits are used extensively, 
particularly around the intermediate 
frequency stage to pass only the frequencies 
in the range of interest. 


THERMAL NOISE 


Thermal noise has a uniform spectrum 
up to 10!3Hz, as white noise does. This 
can be likened to white light which has all 
colours. The noise voltage through a 
metallic resistor is given by: 

V2 = 4KTRB 
where B = bandwidth in Hz 
K = Boltzman’s constant 
T = temperature in Kelvin 
The above equation implies that 





minimum bandwidth must be used to 
transmit the signal in order not to degrade 
the signal to noise ratio. 


Fig.23. Series tuned circuit 


RESONANCE AND 





ENERGY COUPLING 


Resonance may occur in series or 
parallel tuned circuits. In the series tuned 
circuit of Fig. 23, resonance occurs when 


1 


ponent 


Lie 


1 


wL= ee ees 
2m LC 


or f = 


Bandwidth is defined as the two 
frequencies on either side of the resonant 
frequency, at which the power drops to half 
or by 3dB. 

The Q of a circuit is a figure of merit 
and the general definition is: 


27m X maximum instantaneous 
Q= energy stored in the circuit 


energy dissipated per cycle 


PRACTICAL ELECTRONICS AUGUST 1989 





For the series circuit of Fig. 23 


Qq= ME =! 
R B 


where B is the bandwidth. 
In the parallel resonant circuit of Fig. 
24, the same equation applies: 





fz ; 
at LE 
ee ~. = 
B 





Fig.24. 










Fig.24. Parallel 
tuned circuit. 
Fig.25. Single 


tuned transformer. 


The Q of a network can never be greater 
than the Q of the coil. For air cored coils 
the Q is 100 to 200 and for ferrite cores the 
Q is 50 to 100. In the vhf range (30MHz to 
300MHz) helical resonators with a Q of 100 
are used. 

Capacitors behave as series LC circuits 
because of the internal inductance of the 
leads, and radio frequency coils behave like 
parallel LC circuits because of the distributed 
capacitance between the windings. 

Since radio frequency chokes present a 
high impedance, the resonant frequency of 
the circuit needs to be less than the resonant 
frequency of the choke. The cores are 
usually iron, ferrite or phenolic. 

The coupling of energy from one stage 
to another is usually by transformers 
particularly around the intermediate 
frequency (if) stages. The double tuned 
transformer is mostly used around the if 
stage with the single tuned transformer used 
around other stages like the rf stage. 


DETECTOR 


THe 
| 


[0161526] 


‘ a ‘ : OH = a—M—~ = R ” 
tuned transformer. 
Fig.26. Double 


HF RADIO: 





AUDIO 
FREQUENCY 
AMPLIFIER 


The equivalent circuit of a single tuned 
transformer is shown in Fig. 25 and the 
coupling efficiency called the coupling co- 
efficient (k) is given by: 


M 
L;,19 


k= 





The equivalent circuit of a double tuned 
transformer is shown in Fig. 26 and the 
coupling co-efficient is given by: 





M= MUTUAL INDUCTANCE 


Fig.26. 





M= MUTUAL INDUCTANCE 





Fig.27. Self resonant frequency 
range for a given inductor. 









In the next part we shall look 
at the essential parts of a 
radio receiver. Pr 









23 








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PRACTICAL ELECTRONICS AUGUST 1989 25 














robably even before primitive 

man discovered the techniques of 

producing harmonic sounds with 
wind and stringed instruments, he would 
already have known that his body was a 
multipurpose musical instrument. With 
our mouths and vocal chords we can 
produce an astonishing range of musical 
tones, and with our limbs can create an 
equally varied range of percussion 
sounds. 


APPLAUSIBLE 


One of the most frequent sounds we 
produce, whether we are muscial or not, 
is created by sharply bringing our hands 
together, the act of clapping. By 
clapping we can signify many states of 
emotion, ranging from approval or 
disapproval to rhythmic accompaniment. 
Strangely, approval and disapproval are 
differently interpreted by different 
races. In some countries the synchronised 
clapping by an audience signifies ap- 
proval, whereas in others it can be a sign 
of derision. In Britain we seem to prefer 
slow synchronisation for expression of 
dissatisfaction and fast non-synchronis- 
ation, randomness, for approval. All 
cultures, though, seem to be in 
agreement about the use of clapping as a 
rhythmic expression of musical beat. 


designing an oscillator that produces 
pulses on a regular basis. If the pulse 
generator is made to produce clicks at 
different rates, the sound, though 
uninteresting on its own, can serve as a 





allowing the noise to decay in volume 
after the end of the click. We can even 
cater for the simulation of different clap 
reverb times by making the decay and 
amplitude variable. 








In view of the universal use of 
handclapping as a musical beat it is 
perhaps surprising that electronic 
clapping machines have hardly ever 
been published in diy electronics 
journals. Most musical projects have 
been concerned primarily with the 
modification of sounds from existing 
instruments, or the creation of sounds 
that synthesise those of conventional 
instruments. Certainly, rhythm 
generators have been published from 
time to time, but these basically have 
been intended for simulating instru- 
ments such as drums, cymbals and 
gongs. 


MONOTONY 


Producing an electronic simulation of 
hand clapping is not very complex, 
although it takes a fair number of 
components since we ideally need to also 
create ambience, echo and _ tonal 
variation. However, I shall avoid the 
philosophical conundrum of attempting 
to simulate the sound of one hand 
clapping! 

In its most basic form the sound of two 
hands coming together as a clap can be 
created by regularly feeding sharp 
transient pulses into a loudspeaker. In 
other words all you need is a click 
generator. This can be readily formed by 





26 


HAND CLAPPER 


BY HARVEY KENT 


A simple effects 
device which can 
be triggered by 
computer or sig- 
gen, mike or midi, 
or just left to clap 
itself. 


metronome, setting the basic beat which 
other instruments can follow. 

Greater interest can be produced by 
varying the pulse length so that the clicks 
assume a different tone. But the result 
still lacks the reality we usually associate 
with hand clapping. Unless we are 
outside, there is always a degree of echo 
produced by a clap as its sound reflects 
off walls and furnishings, returning to 
the listener at slightly delayed rates. This 
reverberation could easily be produced 
by using an electronic echo or reverb 
unit, but there is an alternative, and less 
expensive method of simulating a similar 
effect. We can give the impression of 
clap reverb by keying in a white noise 
generator at the start of the pulse, and 














SR AN OeNNID ED) amas 


We can also create an even greater 
approach to reality by simulating echo as 
well as reverb. The same technique will 
also give the impression that more than 
one pair of hands is clapping on the same 
beat. Naturally precise synchronisation 
of several pair of hands will never occur 
and so the simulation can be enhanced if 
there is a brief delay between the claps. 
In our circuit then, we must have a 
sequence of pulses, occurring one after 
the other, all triggered by a common 
cause. This train of pulses is then mixed 
together, accompanied by the white 
noise ambience, or reverb, signal. In our 
full circuit we shall want to allow for the 
clapping to be repeatedly cycled through 
under automatic control, or for it to be 
triggered from an external source. 

Having laid down _ the basic 
requirements for a clapping machine, 
let's look at the practicalities. I 
considered two approaches to producing 
a series of clicks triggered by a common 
source, one digital, the other analogue. 


DIGITAL REPEATS 


For the digital approach I could use a 
gated oscillator and a counter such as in 
Fig. 1. The oscillator output is fed to a 





PRACTICAL ELECTRONICS AUGUST 1989 











Fig.1. Digital pulse train generator. 


gate which is controlled by two sources, 
the original starting pulse, and the final 
output of the counter. Each counter 
output has its pulse differentiated by the 
resistor-capacitor networks which are 
fed through to a mixer. The gate opens in 
response to a starting pulse, either from 
another, slower running, oscillator, or 
from an external trigger source. When 
open, the state allows pulses from the 
main osciallator to pass through to the 
counter. Each pulse triggers the counter 
on by one stage, each stage producing its 
own output click. When the counter 
reaches a predetermined output, in this 
case output five, the output causes the 
gate to close. Naturally, no more pulses 
will pass through, and no more clicks will 
be heard. On receipt of the next trigger 
pulse, the counter is reset, the gate 
reopens, and the cycle is repeated. 


ANALOGUE 


COMPARISON 





The analogue technique I have 
enclosed here instead shows how a series 
of comparators can be used to achieve 
the same results. Fig. 2. There are four 
main comparators used, each having a 
different reference level trip point. Each 
comparator output is fed through 
differentiators through to a mixer, as in 
the digital approach. The different 
reference levels are set by a chain of 
resistors coupled as a series of potential 


MIXER 
OUTPUT 





dividers. The voltage level at each 
resistance junction is of course different, 
becoming higher as we move up the 
chain from the bottom to the top. 
Consequently, each comparator will 
only change its output state when the 
input voltage is greater than the 
reference level. If the input voltage were 
to be a sudden change from minimum to 
maximum voltage, all four comparators 
would change state _ practically 
instantaneously. However, if we slowly 
increase the input voltage, there will be a 
delay between each comparator being 
tripped. Consequently, the output pulses 
will be heard as separate clicks. What we 
need, then, is for the starting pulse to 
initiate a ramped change in voltage level. 


RETRIGGER 
CONTROL 
MODE 


SELECT 
O 


Oo—oO 
EXT 


e 
TRIG 
INPUT 
PULSE 
’ | EXTENDER 


So, let’s see how this is achieved in 
practice, in the block and main circuit 
diagrams of Figs. 3 and 4. For the 
moment we will assume that the initial 
trigger pulse comes from an unspecified 
source, through S1 to Cl. ICla is 
configured as a high gain amplifier which 
ensures that even quite low level input 
pulses will be amplified to a maximum 
output level swing. 


EXTENDED TRAINING 


This pulse creates the first of the 
clicks, being differentiated by C5 and 
R13 to pass via D4 to IC3. We'll look at 
IC3 presently. When the output of ICla 
goes high in response to the trigger 
pulse, it also goes via D1 to charge up 
C2. The purpose of this capacitor is to 
extend the effective length of the trigger 
pulse so that we have time to make full 
use of its swing. Although the charge will 
eventually leak away via R39 it will 
remain high long enough for it to be fed 
via VR1 and R5 to charge up R3. The 
rate at which C3 will charge can be 
varied by VR1. The chain of reference 
level resistors consists of R6 to R10. As 
C3 charges up so its voltage level 
successively passes each trip point set by 
the resistor chain. Consequently, each 
comparator trips in a delayed sequence 





Fig.3. Block diagram of clapper effects unit. 


MIXER O 
PUT 


H 
al 
35 


Vs 





Fig.2. Analogue pulse train generator. 


PRACTICAL ELECTRONICS AUGUST 1989 


as discussed above. Each of the four 
outputs is differentiated and fed via 
diodes to IC3. Each trigger pulse thus 
creates five pulses to be delivered to IC3. 

IC3 is a voltage controlled amplifier. 
Ignoring for the moment its other 
control and input sources, [C3 will only 
open when a Suitable voltage level 
appears at its control node pin 5. The 
output will then swing in sympathy 
allowing any signal input to pass through 
to Cll and the volume control VR2. The 
output from VR2 is intended for feeding 
to any normal amplifier system. 


RAMPING SAWTOOTH 


Each of the five generated pulses are 
summed at the junction of D4 to D8, and 
increasingly charge up C4. Between 





27 














R34 100k 


VR4& SOOk R35 10k +VE 
a O 


R37 4700 



















R26 20k 


R38 10k D11 


NO 
CONNECTION 






TRI 


BCS49 








R30 10k 





R17 100k 





100n R3 100k 3 






a 


324 
1C1&2: PINS +VE 

PIN 11 OV(GND) 
IC3: PIN 4 OV(GND) 
PIN 7 +VE 


POWER pe " 
LINE: BETWEEN 9 -15V 











ALL DIODES: 1N4148 








Fig.4. Full circuit diagram of the clapper effects unit. 


each pulse received, R13 causes C4 to 
slightly discharge. Thus the voltage level 
at the junction looks like an increasing 
level sawtooth, and the output from IC3 
will vary accordingly. 

The sawtooth voltage also charges up 
C20 via D10. IC2a then buffers the level, 
and also feeds to the control node of IC3 





28 


at a level set by VRS. The result is that 
even after the sawtooth has ended IC3 
will remain open until C20 has 


discharged sufficiently via R41. 

When all the comparators have 
tripped we need to reset them so that the 
next trigger pulse can repeat the 
sequence. Thus both C2 and C3 have to 





be discharged. The output from the final 
comparator, [C2d, is fed via C15 and D11 
to charge up C19. This causesTR2 to be 
turned on which discharges C2 and C3 
via R37, D2 and D3. The value of C19 has 
been chosen to letTR2 remain open long 
enough to allow adequate discharge of 
C2 and C3. Without C19 you will see that 
TR2 could remain open only until IC2d 
had reverted to its low level state, a 
situation which would not necessarily 
sufficiently discharge C2 and C3. 


matele) NCEOlOn 


Time now to see just what it is that the 
pulse train allows IC3 to pass through to 
the output. For a start, of course, it will 
effectively pass the pulses themselves. In 
the absense of a sufficiently high current 
on it control node pin 5, via either R23 or 
R24, the output at IC3 pin 6 will be low. 
As soon as the current reaches sufficient 
level, the output voltage will rise in 
sympathy. Consequently, the pulse 
sequence will be heard as a sequence of 
clicks, the separation between them set 


by VR1 controlling the ramp rate at C3. 


We said earlier that we also want to 
introduce a certain amount of reverb, or 
ambience simulation from a white noise 


_ PRACTICAL ELECTRONICS AUGUST 1989. — 








C6) Ve) NiaNakS 


RESISTORS 
R2, R12, R31, 





1M (6 off) 










100k (11 off) 


10k (10 off) 









R5,R20,R25, 1k (4off) 
R28 

Ru 10M 

R18, R19,R23,  4k7 (Soff) 


R24, R27 
R26 
R32 510k 

R37 470 

All resistors 44W5% carbon film 




























CAPACITORS 
C1, C4-C9, C12 
2,010, CIS 


100n polyester (8 off) 
22 16Velectrolytic 
(3 off) 
; 1p 63Velectrolytic 

(4 off) 

220p polystyrene 
15n polyester (2 off) 
1n polystyrene 
4u7 63Velectrolytic 





POTENTIOMETERS 
100k mono rotary 
10k log mono rotary 
10k mono rotary 
500k mono rotary 
100k skeleton 















SEMICONDUCTORS 


D1-D1 1N4148 (11 off) 
TR1,TR2 BCS549 (2 off) 
IC1, 1C2 324 (2 off) 


CA3080 


min dpdt 
min spdt 






MISCELLANEOUS 
Pcb clips (4 off), knobs (5 off), 
Phonosonics' PCB293A, 8-pin ic socket, 
14-pin ic socket (2 off), mono jack socket 
(2 off), box 155 x 120 x 45mm. 


Fig.6. Control wiring details. 


SPEED 


PRACTICAL ELECTRONICS AUGUST 1989 


WIDTH TONE 


Serene en aaa DeLedeenebebeaeeeeneneeneanratetenaetetataacetatasatetasetetetatetetetstetetetstetetatesete 


source. Obviously, 1C3 is the place at 
which we introduce it. 


AMBIENCE 





Many of you will know that a reverse 
biased transistor will produce a certain 
amount of noise in response to its non- 
lethal distress under such conditions. 
Some types of transistor will behave 
more noisily than others, but in general 
an npn transistor such as the BC549 and 
its related families can be quite noisy 
under reverse biasing. Note though that 
the noise level can vary between types, 
and even between individuals of the 
same batch. 

TR1 is the source used here, feeding 
the white noise through C14 to the filter 
and amplifier IC1B. The selected 
frequency band of noise is set by C16 and 
C17, and is additionally variable by VR3. 
The latter allows for panel control of the 
ambience tone. The output is fed to the 
input of IC3, with VR6 allowing for 
preset control of the level. 

As IC3 is progressively opened by the 
sawtooth so greater amounts of white 
noise pass through, enhancing the 
ambience of the clap effect. The decay of 
the ambience level then follows the rate 
at which IC3 is closed, depending on the 
setting of VRS. 


TRIGGER CHOICE 


For control of the clapper from 
external sources, the pulses can be 
generated by a variety of devices. One 
possible source is from a microphone. In 
this instance plugging a mic into the 
input and then clapping above it will 
trigger the automatic clap response. 
Alternatively, the pulses could come 
from a signal generator or other 
repetitive pulse producer. And naturally, 
the pulses could come from the output of 
a computer or a midi instrument. 

It is also possible to use the clapper as 
a self contained unit by switching over to 
automatic recycling mode. In this mode 
S1a is switched to the output of IC2a and 
S1b is open. The act of switching from 
external to internal control causes a 






PCB PIN 8 GOES 
TO BATTERY +VE 


AMBIENCE 


AUTO/EXT 








pulse to be generated across ICla, so 
initiating the pulse train. At the end of 
the train, when TR2 opens to discharge 
C2 and C3, it also discharges C18 via D9. 
During the pulse train this has been held 
charged via VR4 and R35. As the charge 
on C18 drops below the reference level 
set by R34 and R36, so the comparator 
IC2a changes its output level state. It 
remains in this state untilTR2 has closed 
and C18 recharged at the rate set by 
VR4. When C18 has passed the trigger 
level in the opposite direction, so [C2a 
again changes state, sending another 
trigger pulse to ICla, and so the cycle 
goes on repeating until S1 is once more 
switched to external mode. 


LIKE THE CLAPPERS 


Construction of the circuit is very 
straight forward and it shouldn't take 
long to put together. Ensure that the 
correct polarities of diodes and 
electrolytic capacitors are observed, and 
that ICs and TRs are in the correct way 
round. The only setting up needed is the 
adjustment of VR6 to allow the white 
noise through at the desired level. The 
panel controls allow for selection of the 
other levels, relative clap rates, spacing 
and tone. The power supply needed is 
ideally suited for 9V battery use, though 
voltages up to 15Vdc could be used 
instead. 

I am sure you will find this circuit an 
interesting addition to your effects line 
up. As a final suggestion, try feeding it 
into a separate echo or reverb unit_as 
well — the results are astounding. 


Don't miss our new 
workshop 
frequency counter 


and dual sig-gen 
test gear project 
next month! 





10 
BATTERY 
-VE (OV) 


4 BATTERY +VE 
6 8 


29 














DATABASE 
pial O Nelms 


Dear John, 

In his March 89 Leading Edge 
column, Barry Fox wrote about 
difficulties in understanding and 
defining relational databases. 

Having tried to grapple with this 
subject from an application point of 
view, I feel it is probably a good idea 
to first study the underlying 
principles, the theory of relations, as 
found in text books on logic. These 
principles are not fundamentally 
difficult. 

Anyone who can understand 
simple expressions like: "Mary (is 
the wife of) William" and "9 (is 
greater than) 5" has already got the 
basic idea. The words inside the 
brackets express the relations 
between the terms on either side of 
them. The relations and the terms 
can be expressed by symbols. 

A non-specialist book I've found 
particularly helpful is An 
Introduction to Logic by Peter 
Alexander, Chapters 2 and 8 
(Unwin, 1971). The author clearly 
explains the various types and 
logical properties of relations. 

Although relational databases are 
a very modern development, the 
underlying theory of relations goes 
back a long way. The British 
mathematician Augustus de Morgan 
(1806-1871), who made valuable 
contributions to symbolic logic 
among other things, was the first 
person to develop relations as a 
systematic theory, in the second half 
of the 19th century. Bertrand Russell 
also wrote on this subject, in 1903. 

Tom Ivall, Staines. 


John (is grateful to) Tom. 


ETHIOPIAN APPEAL 


Dear Sirs, 

It is unfortunate that my 
prodigious interest to have access to 
your monthly publications has failed 
due to the problem of getting foreign 
currency, which is restricted to 
exchange by the government here in 
our country. | 

Since I can obtain your 
publications only intermittently (and 
if not taken by others) from a British 
Council Library here in Addis 


Ababa, I am not always able to enter | 


your competitions. Can you advise 
me of any way in which I can obtain 
your publication on time? 

Moges Belete, Ethiopia. 


We recognise that there is an 
exchange problem for a few 
countries. Some readers with this 
problem have friends in other 
countries who are able to send 
payment on their behalf. With some 


30 





PITCH IN TIME 


Dear Mr Becker, 

As a long time reader of PE and 
dabbler in some of your projects 
over the years, I was interested to 
see your Editorial on vacuum tubes 
in PE Mar 89. I used to run one of 
the departments making valves at 
GEC and little thought to see them 
making a comeback some 30 years 
later, albeit in a rather different 
form. 

It has prompted me to write to 
you for some advice concerning a 
small project which my family has 
been agitating me about for some 
time, but which may require 
someone of 40+ to solve because of 
the technology. 

I have many tape recordings of 
our wedding and other family 
events, such as the children when 
young, made on a now-departed 
reel-to-reel tape recorder bought 
during the late 50s. Wishing to 
transfer them to modern cassettes, I 
recently bought an old 3-speed 
Collaro tape recorder at a jumble 
sale. Having tried my recordings on 
this and other recorders it appears 
that the original machine must have 
been running at the wrong speed. 
At 3.75 ips the voices are pitched 
too low, and at 7.5 ips they are too 
high. Is there some way I can 
modify the playback speed? 
~E.R.Goodwin, West Drayton, 

) Middx. 






countries it is also possible to goa 
local bank and ask for a Stirling 
cheque, drawn against a London 
bank, to be sent to the company 
from whom goods or services are 
required. In your own case it would 
also be beneficial to ask the British 
Council Library for their 
recommendation on how to make 
payment. 

If you are able to find a method 
for making payment, then the best 
way for you to obtain PE ona 
regular basis is to have it sent 
through our subscription service. 
The price is £18.00 per year, for 
which you will receive 12 monthly 
issues. This price includes the cost 
of postage. 

The address to write to is shown 
on the Editorial page. 

Best wishes, 
Ed. 


If your have any comments, 
criticisms or suggestions, 
write and let us know. 
We are interested in what 
you think and say. 












What an interesting coincidence 
about GEC. But who has disclosed 
my age? They were being totally 
mendacious - I'm still only a 
youngster (at heart)! 

Tape recorders of that era 
usually had their speeds controlled 
by the mains frequency of 50Hz (in 
Britain). There are units for 
changing ac power frequency to 
drive equipment like this, but I 
don't know the names of any 
companies who manufacture them. 
Your local reference library may be 
able to advise which directories 
might give the answer. 

Alternatively, you could try 
modifying the inverter shown in the 
Battery to Mains articles of PE Jul- 
Aug 88. If you replace the 50Hz 
generator by another generator 
having a variable frequency, 

you will be able to tune it as 
required. The output current 
discussed in the article should be 
enough to drive the tape recorder. 

There is another, very-low-tech 
possibility. Set the recorder on 3.75 
ips, and wrap layers of Selotape, or 
similar, around the shaft that drives 
the tape transport wheel. As the 
effective diameter increases, so too 
will the tape drive speed. You will 
need to experiment of course, and 
any music may hiccup a bit where 
the Selotape end occurs, but for 
speech it should be ok. I used the 
method myself many years ago, 
while I was still only XX+! 



























Ed 


EAS! ON THE EAR 


I am an aging geriatric whose 
hearing is not as good as it used to 
be, particularly where high notes are 
concerned. To make up for this I tend 
to adjust the tv volume to a higher 
level than that preferred by my wife. 
In addition I have somewhat bizarre 
programme preferences such as 
Open University maths and similar 
arcane subjects which similarly 
distract my good wife's train of 
thought. Have you ever published a 
circuit that will allow personal 
listening without domestic discord? 

Dr R. Parfitt, Croydon, Surrey 





A circuit which might suit you 
both is the Infrared Transceiver 
Headphones project by Robert 
Penfold in PE June 1987. Ed. 





BI NCIO RETAIN T@) 
COMPUTERISSIMO 





Dear Ed, 

Your friendly magazine prompts 
me to write, somewhat belatedly, in 
response a letter published in PE 
Mar 88 concerning automatic bingo 
callers. 

Bingo halls do not exist here in 
Italy, but at festive times of the year 
the family 'tombola’', as we call it, is 
a tradition. A random number 
generator by itself is unsatisfactory 
for serious bingo and would never 
content our bunch of hyper-critical 
moppetts! I agree with you that a 
computer provides a better solution 
than a dedicated circuit design. 

The generator must be capable of 
extracting only integral random 
numbers (no decimal fractions 
allowed) and each number only once 
during any game (no duplication of 
drawn numbers), as well as keeping 
within the limits set by the cards. In 
Italy, tombola has limits of 1 to 90. 
Our answer is to use a short Basic 
program, which we run on a 
Spectrum. 

Thank you for a monthly 'read' of 
sO many topics in the electronic 
environment (satellites to solder- 
tags) where there always seems to be 
something for everyone. 

Ken Jones, Udine, Italy. 


Nice to here from you again. I 
hope the grandchildren are not still 
pulling your leg over our April Ist 
1988 report! 

Ed. 


CHIPPY-CHIPPY 


BANG-BANG 





Dear Mr Becker, 

I want an opamp chip that does 
not damage itself when the output is 
shorted to GND, otherwise a circuit 
diagram that gives protection against 
overload if the opamp is shorted to 
GND. If this is unclear then try this : 
what happens if the output of the 
opamp is shorted to GND? (a) will it 
go BANG! (b) nothing happen (c) 
some makes will goes BANG! while 
other makes don't (d) none of these? 

R.P., Essex. 


Once upon a time, there were 
opamps that would die if their 
outputs were shorted to GND. 
Thanks to the Wizard Hi-Tech, to 
the best of my knowledge all 
modern opamps have their outputs 
protected against short circuits and 
overloads, usually up to the 
maximum voltage permitted for the 
power supply. And they all live 
happily ever after. 

I suggest you read Andrew 
Armstrong's article on opamps in 
PE Feb 88. 

Ed. 


PRACTICAL ELECTRONICS AUGUST 1989 















ELECTRONIC 
COMPONENTS 











NEARLY EVERYTHING ON THESE PAGES IS 


HALF PRICE OR LESS!! 


We must clear last years surplus to make room for more 
So snap up these 


parcels we are expecting soon!! 


unrepeatable bargains now — most goods will not be 


KRAZY 
KEYBOARD 
KLEARANCE 





Z8852 Keyboard: Superb brand new 
keyboard 392 x 181 with LCD displaying 1 
line of 10 characters and a further line 
with various symbols. 100 keys, inc 
separate numeric keypad. Chips on 
board are 2x77HO5, 80C48. LCD + driver 
chips are easily removable from board. 
Looks like it was used with a comms 
package. Has anyone any more info? 
£15.00 


SALE PRICE £7.50 





Z8857 High quality Alphameric keyboard 
on aluminium frame 314 x 150mm. 
Contactless keys good for 20 million 
operations. Originally sold at over £100 
each, they were used in a 'Printcom' 
portable terminal. Fully ASCII encoded 
output. Power supply + 5v and -12v @ 
35mA supplied with comprehensive data. 

£14.95 


SALE PRICE £7.50 





Z8856 Cherry computer keyboard. Very 
slim model 340 x 130 by only 14mm deep, 
including keys. Matrix output. 67 keys in 
pale/dark brown. No idea what computer 
they're from — but they're an absolute 
bargain at only £4. 
SALE PRICE 


£2.00 





Z8848 Keyboard Alpha numeric separate numeric 
keypad. 104 keys. Also chips on board: LS373x2. 


LS374, LM3086x2. 
Size 442x175mm. 
SALE PRICE 


LS138x3, 555, LSO8, 6805. 
£12.00 
£6.00 







Z8863 Keyboard. Hig e by Micro 
Switch 69 pale grey and blue keys. 6 red 5mm 
LED's, 15 various LS chips and socketed D8048 by 
Intel. Output via 7 way plug and there's a 4 way 
edge connector too. Keyboard frame is 317 x 


128mm. PCB on which it's mounted is 285 x 
170mm. Excellent value at £12.00 
SALE PRICE £6.00 


Z4116 24 way (8 x 3) membrane keypad. Large 
(200 x 90mm) area — these were originally used as 
a teaching aid. Overlay template and pinout 
supplied. Now only £2.00 

E £1.00 


Z8833 Tatung VT4100 Keyboard. As previously 
advertised on earlier bargain lists (but these do not 
have a lead attached). New stocks just received of 
this popular cased 85 key with separate numeric 
pad keyboard. Supplied with circuit diagram. 


450x65x125mm. £14.95 
SALE PRICE £7.50 
28842 Also available are some with broken 
keytops (usually 2 or 3) Only £9.95 

£5.00 


SALE PRICE 


Z8835 Keytronic keyboard. We've had these 
before, too, PCB contains MCT210, 7406, INS8035, 
LS373, 2708. 95 x 405 x 180mm. £14.95 
SALE PRICE £7.50 






available once existing stocks are sold!! 

In order to sell at these low, low prices and cover our costs, 
the minimum order value is £10 & postage is £3.00 
regardless of quantity (orders can be made up with non-sale 
goods if required) state "Sale prices" when you order, 
whether by post, phone or fax. See back page for more info. 


CIUIRIRIATH 


neaeaeaol 
& SPEECH 64 





Z4140 New complete set for ZX. Spectrum 
unboxed. (They were bulk packed) £7.95 
SALE PRICE £4.00 


Z4142 Speech 64 for the C64 computer. 
Better thanethe Spectrum version as no 
software needed, and can be programmed in 
plain English! We only have the bare boards 
but these are new and working. A 
photocopy instruction book is included. 

£6.00 
SALE PRICE £3.00 
Z4138 Slot. 'T' connector (1 female, 2 
male) for the Spectrum enabling 2 
peripherals to be connected to one time. 
Further uSlots can be added allowing more 
peripherals to be added: New and boxed. 

£2.00 


SALE PRICE £1.00 


OUR 1389 PAGE 
CATALOGUE + 
SUPPLEMENTS GIVING 
FULL DETAILS OF ALL 

ITEMS IN THIS PULL OUT 
COSTS JUST £1 POST 
FREE BUT WE HAVEN'T 
MANY COPIES LEFT, SO 

BE QUICK! 











~ COMPONENT PACKS - ALL 1/2 PRICE 


C 


GREENWELD — 
THE PACK PEOPLE! 


More packs — more in them — more value! 
All our packs contain brand new, marked 
full spec. components (unless otherwise 
stated) at a fraction of the normal price 
and offer constructors the widest range 
of parts at the lowest cost! How do we 
do it? By buying manufacturers end-of- 
run and surplus components. Because 
we purchase from many sources, we 
have an extremely wide range of top 
quality parts — too costly to sort hence 
the packs described below. Our larger 
packs are ideal for schools, groups or 
clubs. 


SEMICONDUCTORS 


K517 Transistor Pack — 50 assorted full 
spec. marked plastic devices PNP NPN RF 
AF. Type numbers include BC114 117 172 
182 183 198 239 251 255 320 BF198 255 
394 2N3904 etc., etc. 

Retail cost £7+ Special low price £2.75 
SALE PRICE £1.37 


K547 Zener Diodes - Glass and plastic, 
250mW to 5W ranging from 3V to 180V. All 
ready identifiable. 100 for £4.50 
SALE PRICE £2.25 


K537 1.C. Pack — a mix of linear and logic 
chips, from 6 to 40 pin. All are new and 
marked, but some may not be full spec. 


100 £6.75 
SALE PRICE 


£3.37 
K538 Diode Pack — untested small signal 
diodes like IN4148 etc. at a price never 
before seen!! 1000 £2.50 
SALE PRICE £1.25 


K560 Semiconductors — Over the years we 
have purchased many transistors, diodes, 
ICs etc which for one reason or another have 
accumulated in one of our stock rooms. 
Rather than spend weeks sorting and listing 
them, we have decided to make them into 
packs. All components are full spec marked 
devices. Some may be coded. We believe 
this to be one of the best value packs ever 
offered, as many high value components are 
included. Packs are made up by weight; this 
means contents are very approximate — if 
there are several bulky power devices, there 
will be considerably fewer parts than those 
packs containing all small signal items. 


Normally SALE PRICE 

Pack of approx 100 £5.00 £2.75 
Pack of approx 250 £12.00 £6.00 
Pack of approx 1000 £40.00 £20.00 


RESISTORS 


K540 Resistor Pack — mostly 1/8, 1/4 and 
1/2W, also some 1 and 2W in carbon, film, 
oxide etc. All have full length leads. 

Tolerances from 5 to 20%. Excellent range 
of values. 500 £2.50 2,500 £11.00 
SALE PRICES 500 £1.25 2,500 £5.50 


K503 100 Wirewound Resistors — From 
1W to 12W, with a good range of values. 


£2.00 
SALE PRICE £1.00 


K523 Resistor Pack — 1000 — yes, 1000 1/4 
and 1/2 watt 5% hi-stab carbon film resistors 
with preformed leads for PCB mounting. 
Enormous range of preferred values from a 
few ohms to several megohms. 


SALE PRICE 


K531 Precision Resistor Pack — High 
quality, close tolerance R's with an extremely 
varied selection of values mostly 1/4 and 
1/2w tolerances from 0.1% to 2% — ideal for 
meters, test gear etc. 

250 £3.00 1000 £10.00 
SALE PRICES 250 £1.50 10000 £5.00 


Only £2.50 
£1.25 


K505 20 Assorted Potentiometers — All 
types including single, ganged, rotary and 
slider. £1.70 
SALE PRICE £0.85 


K572 Networks 7,8,9 pin SIL; 14 & 16 pin 
DIL. Lots of different values. 
Pack of 100 £4.50 
SALE PRICE £2.25 
K554 Thermistors — Mostly disc, rod and 
some valuable bead types. _Identification/ 
data sheet included. Big variety up to 40mm 
dia! Catalogue value over £50.00 
100 for £8.00 
SALE PRICE £4.00 
K525 Preset Pack — Big, big variety of types 
and sizes — submin, min and std, MP slider, 
multiturn and cermets are all included. Wide 
range of values from 20R to 5M. 
100 assorted £6.75 250 £12.95 
SALE PRICES 100 assorted £3.37 250 £6.50 


CAPACITORS 


K549 Variable Capacitors — Mostly small 
trimmers — airspace, mica and polyprop 
dialectrics, but also included are a few full 
size tuning caps. 25 for £5.75 
SALE PRICE £2.87 


K544 Mullard Polyester Caps — Cosmetic 
imperfections, electrically OK. Wide range of 
values from 0.01 to 0.47uF in 100, 250 and 
400V working. 200 for £4.75 
SALE PRICE £2.37 


K546 Polystyrene/mica/ceramic caps. — 
Lots of useful small value caps up to about 
-01uF in voltages up to 8kV. Good variety. 
100 £2.75 
SALE PRICE £1.37 
K528 Electrolytic Pack — All ready cropped 
for PCB mounting, this pack offers excellent 
value for money. Good range of values and 
voltages from 0.47uF to 1000uF, 6V to 100V. 
£3.95 250 £8.95 
SALE PRICES 100 £2.00 250 £4.50 
K518 200 Disc Ceramic Caps — Big variety 
of values and voltages from a few pF to 


2.2uF: 3V to 3kV. £1.00 
SALE PRICE 50P 


K530 100 Assorted Polyester Caps - All 
new modern components, radial and axial 
leads. All values from 0.01 to luf at voltages 
from 63 to 1000!! 

Super value at £3.95 
SALE PRICE £2.00 
K558 Jumbo electrolytic pack — 10kg of 
screw top computer grade_ electrolytic 
capacitors. Values from 400uF to 83,000pF, 
voltages 15V to 200V. About 40 caps per 
parcel. Value if bought individually over 
£100! Our price? Just £20.00. Order now! 
SALE PRICE £10.00 


SWITCHES & RELAYS 


K520 Switch Pack — 20 different assorted 
switches — rocker, slide, push, rotary, toggle, 


micro etc.... Amazing value at only £2.00 
SALE PRICE £1.00 
W4700 Push Button Banks - An 


assortment of latching and independent 
switches on banks from 2 to 7 way, DPCO to 
6PCO. A total of at least 

40 switches for £2.95 100 £6.50 
SALE PRICES 40£1.50 100 £3.25 


K532 Relays — Wide selection of styles 
voltages and contacts. 4v-240v, AC/DC, SP 
and 4PCO 20 for £6.00 
SALE PRICE £3.00 


K542 Reed Relays 

Mostly DIL, single pole & double pole also 
some changeover, these are manufacturers 
rejects, but a good proportion work. 5V-50V 
Coils 50 assorted £3.30 
SALE PRICE £1.65 


K569 Reed Switch Pack. A selection of 
about 15 types of reed switch from submin 
12mm long to 5A rated 50mm long, mostly 
form A (make), few form C (Changeover). 
Pack of 30 £2.75 
SALE PRICE £1.37 


OPTO 


K539 Led Pack — not only round but many 
shaped leds in this pack in red, yellow, 
green, orange and clear. Fantastic mix. 

| 100 £5.95 250 £13.50 
SALE PRICES 100 £3.00 250 £6.75 


K524 Opto Pack — A variety of single point 
and seven segment LEDs (incl. dual types) 
of various colours and sizes, opto isolators, 
numicators, multi digit gas discharge 
displays, photo transistors, infra red emitters 
and receivers. 


SALE PRICE 


25 assorted £3.95 
£2.00 


HARDWARE 


K551 6BA screws -— In a variety of lengths 
and heads from 3/16" to 20mm long. Steel. 


200 £2.00 
SALE PRICE £1.00 


K559 Knobs — Wide selection of sizes, 
shapes and styles for various diameter 
shafts and sliders 25 for £1.95 
SALE PRICE £1.00 


K535 Spring Pack — approx. 100 assorted 
compression, extension and torsion springs 
up to 22mm dia. and 30mm long £1.70. 
SALE PRICE 85P 


K571 Cable Clips — 6 or 7 different sizes 
from 3.5mm to double T & E mostly black 
and grey. 100 assorted 99p 
SALE PRICE 50P 


K564 PCB stand-offs. A mixture of 8 
different styles and sizes from 4.75 to 
12.7mm high. 100 £2.40 
SALE PRICE £1.20 


K567 Wire Ties. 5 types to take 4-15mm 
dia cable bundles. 100 £1.70 
SALE PRICES 85P 


K565 Miniature PCB supports in nylon. 6 
different styles — sizes from 6.35 to 13.24mm 
high. 100 £2.20 
SALE PRICE £1.10 


K566 Self adhesive cord clips in moulded 
nylon. 5 styles/sizes. Base size from 15.9 to 
31.8mm square 


SALE PRICE 


Pack of 100 £2.70 
£1.35 


K568 Giant Plastic Pack Approx. 1000 
pieces — standard and miniature PCB 
supports, self adhesive ribbon cable clips, 
straps, ties, cord clips. This lot would 
normally cost around £50.00 

Our Special Price £12.00 


Sale price £6.00 


KS63 Cable markers (ident sleeving). Over 
1000 pieces, all with either letter or number. 
Assorted colours and sizes from 1-5mm dia. 
over 50 different! 


SALE PRICE 


Pack of 1000 £2.50 
£1.25 








Z497 AM/FM Stereo Tuner Panel. 


Complete radio 
chassis with push-button selection for LW/MW/FM and 
ON/OFF. Ferrite rod for LW & MW selection, co-ax 
socket for FM aerial. Supplied with mains transformer 
and rectifier/smoothing cap, and wiring details. PCB is 


330 x 90mm. Reduced to £7.95 
SALE PRICE £4.00 


1W Amplifier — mono 





Z914 Audio amp panel 95x65 
Gives 1W output ‘with 9V supply. 
control. Just connect batt. and speaker. Full details 


mm with TBA820 chip. 
Switch and vol. 


supplied. Only £1.50; 10 for £12.00; 
25 for £25.00; 100 for £75.00 
SALE PRICES 75p each; 10 £6.00; 


25 £12.50; 100 £37.50 
1W Amplifier — stereo 


Z915 Stereo version of above 115x65mm featuring 
2xTBA820M and dual vol. control. 

£3.50, 10 for £30, 

25 for £65, 100 for £200 

£1.75, 10 £15, 

25 £32.50, 100 £100 


SALE PRICES 





Z974 Mixer Amp Panel — 115x115mm and gives 1W 
O/P from a TBA820M chip. There are two inputs, one 
via a pre-amp, from phono sockets and separate 
volume controls. A third pot is used to fade from one 
input to the other. There are also 2 4p 3w rotary 
switches. Attached to the PCB by flying leads is a 
panel on which are mounted the 2 input skts, 2x5 pin 
DIN skts and 2 pin DIN speaker skt. A data sheet is 
supplied All this for just £2.50 
SALE PRICE £1.25 





Z4134 Speaker remote control box. This is a cream 
case 125x95x42mm housing a 57mm dia speaker and 
2 control knobs, one for volume and one to switch 
main-remote-dual, the 3 core 6m long lead enables 
volume to be controlled from chair or bed. Simple to fit, 
instructions included. £3.95 
SALE PRICE £2.00 





24135 'STETHOPHONE' mini stereo head-phones, 
complete with stereo jack plugs, 8R. Hinged 
headband. £1.75 


SALE PRICE 87P 


Hi-Res Monitor 





Brand new and boxed, complete apart from case, the 
super high definition (1000 lines at centre) makes this 
monitor ideal for computer applications. Operated from 
12V DC at 1.1A. Supplied complete with circuit and 2 
pots for brilliance/contrast + connecting ‘instructions. 
Standard input from IBM machines, slight mod (details 
included) for other computers. 

Price £24.95 4 for £99.00 
SALE PRICE £12.50; 4 FOR £45.00 
7494 Newbrain Motherboard. Micro-processor panel 
265 x 155mm. Complete PCB for computer, Z80, 
EPROM, etc. 68 chips altogether + other associated 
components, plugs, sockets, etc. Brand new in original 


packing. EO.00 
SALE PRICE £2.75 
2672 Newbrain motherboards. Complete but probably 
faulty. £3.50 
SALE PRICE £1.75 


2620 68000 PANEL PCB 190 x 45mm believed to be 
from ICL's ‘one per desk' computer containing 
MC68008P8 (8MHz 16/8 bit microprocessor) + 4 
ROMs all in sockets. TMP52220CNL, 74HCT245, 
HCT138, LS38 & LS08, also 2 x 20w SIL sockets & 2 x 





14w SIL sockets. £5.00 
SALE PRICE £2.50 
Set Top C rter 





Z8828 Made by Thorn EMI, this was used to receive 
cable television. 2 part aluminium case 
211x158x82mm (no front panel) contains 2 PCB's: (a) 
control board with multiway switch, dual 7 seg plug in 
display, couple of chips. (b) main boara with mains 
transformer, tuner, RF section etc. Rear panel has input 
and output sockets. 2m mains lead with moulded on 
13A plug. £9.00 
SALE PRICE £4.50 





Z803 Auto Dialler. Sloping front case 240 x 145 x 
90/50mm contains 2 PCBs: one has 4 keypads (total 
54 switches) + 14 digit LED display. 2xULN 2004, 
ULN2033 and 4067; the other has 12 chips +4 power 
devices etc. Case contains speaker. For use with 
PABXs, could probably be modified for exchange line. 


Needs 12V ac supply £9.00 
SALE PRICE £4.50 
Prestel Unit 





7819 Brand new and boxed, complete with co-ax T 
connector, aerial lead and instruction book. Only one 
snag — the remote control hand-set is missing. Size of 
smart wooden case is 347x187x100mm. Mains 
operated. Old style BT plug. Made by Ayr Electronics, 
Model P £22.00 
SALE PRICE £11.00 





Z8862 Video game unit with 10 games, utilizing, the 
AY-3-8610 chip. Consists of 2 handheld units 145 x 60 
x 45mm made of light and dark grey high impact 
plastic. Unit 1 has a control panel with 0-9, serve and 
reset buttons, 3 switches for bat size, ball speed and 
sound on or off, and built in joystick. Unit 2 has a serve 
button and joystick. the two units have 2m of 5 core 
cable between them, and the 3m lead from unit 1 has 3 
x 3.5mm plugs; 1) 7-5V input; 2) audio out; 3) 
composite video out. Worth what we're asking just for 


the cases! £9.95 
SALE PRICE £5.00 


Dual Sheet Feeder 





28837EXXON DUAL SHEET FEEDER Z200. Overall 
395x210x285mm. Brand new and containing some 
very high class electronics. although of little practical 
use as it stands, it makes a great break down unit. It 
contains: 

3x12V 36R 7.5° stepper motors by Airpax and 
associated gear trains drive belt etc. 

2x12V Solenoids 

1x12V electronic buzzer 

2 extremely sensitive micro-switches. 

1 PCB containing 4xTIP115, 4xTIP110, 2x7407, 
LM3302 comparator + T's. R's, C's, plugs, sockets etc. 

1 control panel containing 4 LED illuminated push 
buttons + green LED on small PCB 

1xOPB703A opto coupler 

1xOPB7111 opto coupler 


Obviously, a very expensive piece of machinery to 
produce — but once again our contacts in the trade 
have enabled GREENWELD to procure a few hundred 
for a fairly modest sum, allowing us to offer them at the 


bargain price of £24.95 
SALE PRICE £12.50 
Touch Pad 





2811 Cumana Touch Pad for the BBC computer. This 
remarkable add-on enables you to draw on the screen 
using a stylus with the touch sensitive pad. Supplied 
with 2 stylii, power/data connecting lead and demo tape 
with 4 progs. Contains state-of-the-art electronics. 
Originally being sold at £79.95 — but we can offer a limit 
quantity of these brand new and boxed for just £19.95 
SALE PRICE £10.00 


Fibre Optics 





Scoop purchase of single and twin cable. For use with 

visible light or infra-red. Core 1mm dia, overall 2.25mm 
dia. 

Single 50p/m; 20m coil £4.00 

Twin 90p/m; 20m coil £6.00 

20M SINGLE £2.00 

20M TWIN £3.00 


SALE PRICES 





@ 9 





the electronic football game of skill 





2817 
game — Waddingtons' ‘JIMMY’. 
Brand new models in full working 
order, but without plastic peripherals, 
stickers etc. Red plastic case 420mm 
long x 93mm wide contains keypad 
and seven segment LED's to keep 
score either end. The centre section 
‘players’ are represented by red 5mm 
LED's, 14 altogether. The main chip 
is the TMS1000, programmed to 
make odd noises whilst playing and a 
tune when a goal is scored. Also 
inside are 13 plastic transistors, 
o/mm 8R_ speaker, power supply 


Exciting electronic football 


socket, R's, C's etc. Powered by 
2xPP3 batts. Solo or dual play. 
Supplied with instruction sheet, 


playing field complete with coloured 
‘players'. Good fun to play as a game 
and good value for the electronics 
within. Originally retailed at £19.95. 
Only £5.00 


Sale price £2.50 
SPEECH CHIPS 

SPO256A Only £1.00 
10 for £7.00 100 for £50.00 

OTHER SEMICONDUCTORS: 


See pages 82-83 of catalogue 25% off 
all prices!! 


POWER FET'S 


Pair of 140V 100W Hitachi devices 
2SJ49 & 2SK134 . List price £10.72 


Price £6.00 





SWITCH 








ASTEC Model AA12531 
/P: 115/230V ac 50/60Hz 
O/P:V1+5v 5A 

V2 +12v0.15A 
Size: 160 x 104 x 45mm 


Partially enclosed panel with fixing 
holes in steel case on 120 x 125mm 
centres. 


Inputs and Outputs are on colour 
coded leads; there is also an EEC 
socket on a flying lead. 


£6.95 


KNOCKOUT KNOBS!! 


Sim to K9 — 19mm high x 20mm dia 
with coloured tops. 
Pack of 25 £3.00 


DISK DRIVE PSU KIT 


Ideal for powering single 3 1/2" or 5 
1/4" drive. Mains input, stabilized 
smoothed outputs, 5V@1A + 12V@1A. 
Simple, easy to assemble kit with 
all parts and full instructions. £4.95 


PHONE YOUR ORDER 
THROUGH NOW - VISA & 


ACCESS ACCEPTED. 
(0703) 772501 





1989 CATALOGUE SALE PRICES BY PAGE NUMBER 


P1-18 10% off P72 
P25 10% off P73 
P31-34 10% off 

P35-36 5% off P74 
roo 10% off P75 
P57-59 10% off P76 
P62-63 20% off P77 


BARGAIN LISTPAGES P78 
P68 _—Alll 1/2 price P79 
P69 All 1/2 price 
P70  SB17 £1.00 P81 
78827 £2.00 P82-83 


Hi-Res Monitor P84 
£12.50 P85 
SB14 £1.50 P86 
All 1/2 price 


All 1/2 price P87 
All 1/2 price 

except SB15 P88 
All 1/2 price P89 
All 1/2 price 

All 1/2 price 

All 1/2 price 

All 1/2 price 

All 1/2 price 

P80 All 1/2 price 

All 1/2 price 

25% off 

All 1/2 price 

All 1/2 price 

All 1/2 price P93 
except joysticks P94 


Relays 25% off — 
Rest 1/2 price 
All 1/2 price 

All 1/2 price 
except: 

24072 25% off 
Z656 25% off 
Z802 20% off 
All 25% off 

All 25% off 
24100 £2.00 
2488 £2.00 
J001-3 £1.20/10 
Rest 1/2 price 
All 1/2 price 

All 1/2 price 


1989 SPRING SUPPLEMENT SALE PRICES 


10% off 

10% off P24 
10% off 

20% off P25 
All 1/2 price 

28858 20% off 

24167 20% off 

28861 20% off 


Rest 1/2 price P26 
SB10 £2.00 P27 
Rest 1/2 price 

24162 20% off P28 
24163 20% off P29 
24164 Sold out P30 
SB6 Sold out P32 
Rest 25% off 


All 25% off 
Z8862 1/2 price 
Rest 25% offf 
All 1/2 price 

All 1/2 price 
10% off 
Headphones all 
given away 





ODE PSU BARGAINS 











ASTEC Model AC9231 
VP: 115/230V ac 50/60Hz 
O/P: 50Watt max: 
V1+4+12v2.5A 

V2 +5v6.0A 

V3 12v 0.5A (+ or -) 

V4 5v 0.5A (+ or -) 


Size: 203 x 112 x 60mm 


Fully enclosed case with built in tapped 
mounting holes. 


Inputs and Output pins on edge of 
panel. 


£9.95 
VEROBLOC 


AMAZING OFFER!! 
RRP £6.69 


ONLY 


£4.95 
ANTEX 


All Soldering Equipment 
15% off!! 


SOLDER 


16g 500gm reels resin-cored solder. 
Only £3.95; 10 reels £33.00 









GREENWELD 


ELECTRONIC 
COMPONENTS 






443C MILLBROOK ROAD, 
SOUTHAMPTON, SO1 OHX. 


ORDERING INFORMATION 
All prices include VAT; just add 


£3.00 P&P; Min order value 
£10.00. Official orders from 
schools welcome — Min _ invoice 


charge £10.00. Our shop has 
enormous stocks of components 
and is open 9-5.30 Mon-Sat. 
Come and see us! 


HOW TO CONTACT US: 


By post using the address above: 
by phone (0703) 772501 or 783740 
(ansaphone out of business hours); 
by FAX (0703) 787555; by E Mail 
Telecom Gold 72:MAG36026; by 
Telex 9312131093 (GWG) 












« MARINE ELECTRONICS: 


signal-noise is 20dB, sensitivity 2V, and the 
image ratio better than 60dB. Evaporated 
aluminium dry recording paper is used for 
high contrast without odour or dust, and is 
activated by a single stylus. 


NAUTEX AND SEA FAX 











dedicated video navtex receiver from 
Nasa Marine edits and sifts the 
information, accepting and _ storing 
messages only of the types of information and 
from which stations you have defined. The 
system has a high contrast data display screen 
and is based on a 68000 series microcomputer 
using the latest version of Alnor error 
correcting software. Lokata have a model 
using software routines which error-correct all 
messages before printing, and ensure that no 
message already received is reprinted. 

The error correcting software seems as 


RADIO DIRECTION 


IN DING 





A low cost handheld rdf is available from 
Nasa Marine. It comprises a receiver covering 
180-400kHz, headphones and a compass. The 
rdf beacons can be identified by their morse 
code signatures and the unit is simply turned 
though it must be incredibly intelligent and and tuned until a null is received from the 
sophisticated - I wonder how garbled desired one, and its compass bearing noted. 
messages are correctly interpreted without  - Readings are taken for three beacons, their 
semantic error? Even the word processing directions plotted on the chart and normal 
software with which I'm writing now needs triangulation determines the user's position. 
human intervention on its spell checking An rdf that can be manually or 


routines (especially for its Americanisms - Hand held global position automatically operated and covering a variety 
ha!). sensor of vhf channels is manufactured by Furuno. 


BOATING 
REVOLUTION 











Fax is now also all at sea (was it ever BY JOHN BECKER The selected channel and the bearings of 
not?!). ICS Electronics is one of several incoming signals from ships, coastal stations 
companies offering radio facsimile. Their Fax and emergency position indicating radio 
1 machine has a rtty receiving terminal, # beacons (EPIRBs) are shown on an Icd 
handles Navtex, and prints out high quality Concluding our display. It covers channels AO, Al, A2, 
weather maps, cloud cover photos and news international vhf (1-28, 60-88 ship or coast), 
reports from .around the world. This report on how Scandinavian fishing channels’ (Fl 
information is of use not only to professional i = 155.6325MHz - Ch52, F2 155.775MHz - 
mariners, but also to small boat owners, Neptune S domain Ch55, F3 155.825MHz - Ch56), pleasure craft 
farmers, aviators and many others who have Po - = channel F4 (155.525MHz -Ch50), US 
outdoor interests. The Fax 1 requires the use IS turning hi-tech weather (W1 162.55MHz - Ch39, W2 
of a standard communications receiver and a 162.40MHz - Ch36), and distress channel 48 





computer printer, such as an Epson FX80 (121.5MHz). (I've given all these figures in 
compatible with parallel interface. ———@ ———_————————____—_ case anyone wants to try a bit of 
The rtty baud rates catered for are Weather maps can be directly received via many | ;dxing) 
45, 50, 75 and 100, with rtty radio fax models 
frequency shifts of 425Hz and |... 
850Hz. The audio input can be from 
15mV to 2V rms. a -—C 
Furuno's fax receiver FAX208A { =~ 
takes all known 80-1650kHz and 2- : :  - 
25MHz fax frequencies. It has ten  _—CsSCs . _ Ampro offer a handheld GPS 
additional channels for user | : . which reads signals from satellites 
programming, a Navtex option, and and computes the information to 
a maximum capability of 371 determine the exact position 
channels. anywhere in the world. It displays 
Weather chart printouts which lat/long, range, bearing, speed and 
show cloud pictures in eight shades course over ground, and cross track 
of black can be produced by the error. An alphanumeric keypad 
Koden FX7181. It uses a fully allows the user to show way points 
automatic pll synthesised double- by name, can store 50 of them, and 
superhet receiver with an automatic has an auto position fix when started. 
start-print-stop action responding to The size is 8.75 x 3.5 inches, and it 
standard WMO signals. Up to 23 weighs only 1.5 pounds. Originally 
frequencies can be preset within the developed by the US government, it 
ranges 80-200kHz and 2-25MHz. has now been released to the 
There is a manual channel function professional and leisure market. 
selectable in 100kHz steps, the The international aviation distress 





GLOBAL 
mOS HONING 


PRACTICAL ELECTRONICS AUGUST 1989 Bn) 








A very portable radio direction 
finder 





frequency of 121.5MHz is _ constantly 
monitored by commercial aircraft, the search 
and rescue satellites Cospas and Sarsat, and 
the majority of RNLI rescue craft which are 
also fitted with vhf/rd equipment. In an hour, a 
Nimrod aircraft can visually search only 1800 
square miles; with radar it can cover 65,000 
Square miles, but if a distress beacon is being 
sought 384,000 square miles can be covered. 

The Cospas/Sarsat system was put into 
operation in 1982, additionally monitoring on 
406MHz, and typically offers a beacon 
distress location finding accuracy to within 2- 
Skm. The system has the capability for a 
satellite to simultaneously monitor 90 beacons 
within its view. 

Globally, mariners in distress can transmit 
directly to the satellites which retransmit the 
call to ground receiving stations, known as 
local user terminals (LUTs). In the UK, one is 
based at Lasham. The ground station 
processes the signal, records the location and 
passes it on to a mission control centre (MCC) 
- in the UK it is at Plymouth. MCC then sends 
the location to the appropriate land/sea rescue 
coordinating centre (RCC), and the rescue 
operation is commenced! 


DISTRESS CODING 


In 1979 the World Administration Radio 
_ Conference (WARC-79) recognised _ the 
limitations of the 121.5MHz system and 
allocated the new distress frequency channel 
on 406MHz. The channel is very stable and 
uses pulses which are phase modulated with 
digitally encoded messages. The transmission 
signal itself enables a distress location to be 
established, but in addition, the coded 
messages can provide information such as the 
vessel's country of origin and the nature of the 
distress. For example, (1) fire/explosion, (2) 
flooding, (3) collision, (4) grounding, (5) 
listing/capsizing, (6) sinking, (7) disabled and 
adrift, (8) abandoning ship. 

Jotron's distress. beacon, Tron 30S, 
operates on the 406MHz channel but also has 
the option for transmitting on the homing 
frequencies of 121.5MHz and 243MHz. It has 
90 hours operational time, and incorporates a 
flash light. Lokata have their 406P(X) beacon 


36 








which includes the unique user selectable 
message capability, and also  has_ the 
121.5MHz homing signal for air/sea rescue 
services. Swiftech's GL90 operates only on 
the 121.5MHz channel but can be detected at 
30,000 feet within a 200 mile radius. It is 
small enough to be attached to a life jacket or 
linked to a crew member by a lanyard, and it 
floats. It is lithium battery powered, with a 
Shelf life of up to ten years. 


INMARSAT 





The International Maritime Satellite 
Organisation, Inmarsat, operates a system of 
satellites to provide telephone, telex, data and 
facsimile, as well as distress and safety 
communications services, to the shipping, 
aviation and offshore industries. Unlike some 
other communications systems, Inmarsat's 
links are unaffected by storms, sunspots, 
ionospheric or other radio propagation 
conditions, or congested traffic lists. With this 
system it is not only virtually impossible to 
eavesdrop on the content of transmissions, but 
also competitors cannot tell when or from 
where you are transmitting. (In the maritime 
business, often the ability of the competition 
to detect and locate a radio transmission is 
sufficient to give your secret away!) 

Inmarsat began operations in 1982 and by 
the end of 1988 over 7700 ship earth stations 
or transportable versions were using the 
system. In the Standard-A system, Inmarsat 
operates via eight satellites in geostationary 
orbit, located above the Atlantic, Pacific and 
Indian Oceans at an altitude of 36,000km. 
They provide coverage of almost all of the 
world's surface, except the extreme polar 
regions. Of these eight, three are prime 
operational satellites and the others are 
maintained as "hot" spares. 

Inmarsat are about to acquire a second 
generation of satellites, the first four of which 
are to be launched during 1989, and will 
become part of the new Standard-C system. 

Standard-C will use a new range of 
microterminals. These will be light weight, of 
only a few kilos, and compact enough to be 
fitted to aircraft, vessels and land-based 
vehicles of any size. Some units are planned 
which will be small enough to be handheld, 
and fit in the pocket or handbag. As well as 
being of obvious benefit to commercial users, 
Standard-C units will have a powerful impact 
for office and personal users. In addition to 
offering position reporting data, they will 
enable two-way communications between 
mobile users and their homes or offices, on a 
global basis. 

Information on the handheld units is not 
yet available, but at least one company has 
Standard-C terminals for marine users. Thrane 
and Thrane have a low cost unit, the 
TT3020A, whose applications range from 
merchant ships to private craft. | 

With the introduction of the new Standard- 
C service imminent, marine and land-based 
communications are on the threshold of one 
of the most exciting developments for many 
years. 





This emergency radio beacon 
just clips to a life jacket 


MICRO-RULING 


THE WAVES 





Britain has long been a nation of boat 
owners. As one who observes the scene mainly 
from the shore, I believe that traditionally, boat 
Owners have been conservative about 
introducing new technology. (Correct me if you 
think I'm wrong!) That appears to be changing 
rapidly. In so many areas of society, electronic 
technology is finding broader acceptance and 
this is permeating into the leisure marine 
market as well. There is no doubt that, as I said 
in the introduction, the coming of micro- 
computers and  sub-miniature _ electronic 
devices is facilitating the expansion of marine- 
orientated electronic products. Britain has one 
of the largest areas of boat parks in Europe, and 
most craft in them are fitted with some of the 
latest marine instruments. Currently, marine 
electronic products can account for some 30% 
of a boat's total cost. 

Regrettably, it is obvious that there a few 
manufacturers who believe in charging what the 
market will pay rather that what the product is 
actually worth. Some prices are much higher 
than I feel is reasonable. Nonetheless, the 
situation is changing. The 1980s saw the start of 
the boom in hi-tech marine control and 
monitoring for the leisure market. With more 
manufacturers now producing such products, and 
with more leisure boat owners wanting them, the 
prices will undoubtedly fall in real terms. 

PE will keep a weather-eye on the trends 
and, from time to time, update you on their 
progress. Let me know how much this overview 
of marine electronics has interested you. WD 





If anyone would like a list of relevant 
manufacturers and suppliers who were 
at the Boat Show please send a small 
stamped addressed envelope to me at the 
Editorial address. 







PRACTICAL ELECTRONICS AUGUST 1989 












SPECIAL PURCHASE FLOPPY DISK DRIVES 2 POWER SUPPLIES 
V22 1200 baud modems BARGAINS GALORE ! All power su rate from 220-240vac. All power 


les o 

supplies are BRAND EW unless stated. We have many 
Ye got a tremendous buy on further stocks of this popular Ai ! ther types i 3v stock. 
laster Systems 2/12 microprocessor controlled V2 full ct NEW 5% inch from £29.95! . ab ek ee a tb 


duplex Massive . 

: purchases of standard 51/4" drives enables us to Byte Drive BD301Dual output Svdc @ 1.6 amp & 12wWe@ 1.5 
ana a Fully ST peas vali oa a tee Libel present prime product at industry beating low prices! All units amp. Perfect for disk drives. Has standard Molex sockets.Attrac- 
DS inh scoed data pda Which at 120 . us tan cave your Unless stated) are removed from often brand new equipment tively encased. Dim 15 x 12 x 7 cm. £19.50(B) 
hone bill and connect time by a staggerin 5%l Ultra aa 45 and are fully tested,aligned and shi to you with a 90 day Plessey PL122 fully enclosed 12vde 2 amp. Regulated and 
m high. Full featured with LED status indioators and remote guarantee and operate from +5 & +12vde, are of standard size short proof. Dim 13.5 x 11 x tem. E1G05(G) 

rror diagnostics Sync or Async use; ch or data switching; and accept the standard 34 way connector. AC-DC Linear PSU with outputs of “Sv @ 5.5a,-Sv @ Nie 
hin oAOy ee as at p veep eye rection to BT Une SHUGART SA405. BRAND N £29.95(B) -24v @ 5a. Fully regulated and short circuit proof. Dim 28 x 12.5 
re inused but good condition. Fully tested prior despatch with TANDON TM100-2A IBM compatible DS £39.95(B) xf sa i apap 
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wae rir papl lb : £69 (D) CANON, TEC etc.DS half height.State 40 or 80T £75.00(B) Boshert 13090 switch mode ideal for drives or complete system. 
P ONLY TEAC FD-55-F.40-80 DS half height. BRAND NEW £99.00(B) = @ 6a +1 2v @ 2.5a, -12v @ 0.5a and -5v @ me Os 5.6 

x x 10.8 cm. 95 
MONITORS 316 INCH BRAND NEW AT £19.95!! Soenert 13085, Same as above but outputs of +5v @ 64,+24V 
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COLOUR MONITORS to be by Canon. Brand new and packaged - mint condition! 40 Greendale 19ABOE 60 watt switch mode outputs -5v @6a,+12v 
becca 16” 80 series budget range colour monitors. Features track SS, run from +5 & +12vde with standard power connec- @ 1a,-12v @ 1a,+15v @ 1a. Dim 11 x 20 x 5.5 cm. Removed 


































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lly tested surplus, sold in little or hardly used condition with 90. Shugart 851 double sided refurbished & tested  £195.00( Farnell G6/40A Compact 5v 40a switch mode and fully 
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Lowest ever priced 8 mhz PC-AT 286 clone with 20 mb hard 


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3 inch AC. 11" thick £ 8.50(B 
MONOCHROME MONITORS 312inch AC ETRlslimline.Only 1” thick. £ 3956} 5 : TV SOUND 

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ng only 11.6H x 12W x 22D. Ideal for CCTV or computer 4inch AC 11" thick £ 9.95(B i: 3 TUNER! 
applications. Accepts standard composite or individual H & V 10 inch Round.314 thick. Rotron 110v £10.95(B ' 
syncs. Needs 12vdc at only 0.8a. Some units may have minor 62 mm DC 1" thick. No.812 for 6/12v.814 24v. £15.95(A) Brand new high quality, fully cased, 7 channel UHF PAL TV tuner 
screen blemishes. Fully tested with 30 day guarantee and full 92 mm DC 12v. 19 mm thick. £10.95(A) system. Unit simply connects to your TV aerial socket and colour 
data. £29.00(C) 4 inch DC 12v. 12w 11" thick £12.50(B) video monitortuming same into a fabulous colour TV. Dont worry 

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VC 751 ultra compact chassis monitor for 12vdc 0.7a. Dim { RECHARGEABLE BATTERIES for Headphones a Hi Fi system etc. Many other rae LED 
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DO” Bleck & white monitors by Aztek, Cotron & National. Ail ,. Maintenance free sealed long life, all type A300. Supplied BRAND NEW with full 1 year guarantee. 
solid state, fully cased monitors ideal for all types of AV or CCTV hha - pele 3 amp/hours aN Telebox ST for composite video input monitors......... £29.95(B) 
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audio amp and speaker. Soldin good used condition - fully tested volts Centre tapped 1.8 amp hours (A) Telebox RGB for analogue RGB monitors.................£59.95(B) 

th 90 day guararmee. £95.00(F) SPECIAL OFFER! NOT suitable for IBM clone type colour monitors. 

IBM KEY BOARD DEAL 100 amp/hours at 6 volt! Brand new Chloride Powersafe é 
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\ replacement or backup keyboard for IBM PC, PC-XT or for uninterruptable power supplies, portable power source, , 
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a deall C RAND NEW AND BOXED ONLY ¢59 (B) F size Zah 6 for £8(B Centronics 150 series. Always known for their reliabilty in con- 
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ntegral TEAC 5.25 80 track double sided disk drives. Generous 
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: yne Kerr RA200 audio real time freq.res.analyser. 
Serial and parallel Sagi yh full pearly meg 64K ram and Tektronics 1411/R PAL TV test signal standard 
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eo. ©  e0e, cece. 2 eco eo © 
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All prices for UK Mainland. UK customers AD : 
me-minimum account order £25. Carriage charges (A)=£1 .50. (B)=£3.50. (C)=£6.50. (D)=£8.50. (E)=£12.50 (F)=£15. (G)=Calll . All goods supplied subject to our | 


standard Conditions of Sale and unless otherwise stated guaranteed for 90 days. All guarantees given on a retum to base basis.We reserve the right to change prices & | 
specifications without prior notice. Orders accepted subject to stock. Quotations willingly given for higher quantities than those stated. | 


-Electronics- 


| PRACTICAL ELECTRONICS AUGUST 1989 37 








JUNE 1989 











NEW 
CAT 
OUT 
NOW! 


Over 3,000 product lines 
feature in the Summer 1989 
edition of the _ Cirkit 
Constructors’ Catalogue, 
available from most larger newsagents or direct from the company 
priced at £1.50. The latest books, an RF frequency meter, two new 
PSU designs and a 3.5MHz converter are among the innovative new 
Kits this issue, while our construction project - a 2 Watt stereo 
amplifier - is bound to prove an absorbing activity for dedicated 
constructors. In the test equipment section there’s a whole new 
range of multimeters, a bench DVM and a triple output PSU. 

For eagle-eyed readers who enjoy a challenge of a different sort, 
there is the opportunity of winning an audio signal generator worth 
more than £180.00 In the latest fiendish competition. All prices now 
include VAT for quicker, easier ordering; and Cirkit’s same-day 
despatch of all orders, combined with value-for-money discount 
vouchers, makes the line-up even more attractive. 


D-MM GOOD VALUE! 


Cirkit's six new digital 
multimeters are packed 
with sophisticated extra 
facilities: Capacitance 
measurement, frequency 
measurement up to 
20MHz, temperature 
reading, transistor test 
and logic test in addition 
to the usual volts, current 
(DC and AC) and 
resistance measurement 
- and all unbeatable 
value with prices ranging 
from £20.00 to £55.00! 






























38 














CRE. SRO MOQHGWIWN. FH GGG 


wk 
S SRL 


— 


-oo IN ONE GREAT KIT! 


The K5000 Metal Detector Kit combines the 
challenge of DIY Electronics assembly with the 
reward and excitement of discovering Britain’s buried 
past. 


THE KIT — simplified assembly techniques require little 
technical knowledge and no complex electronic test 
equipment. All stages of assembly covered in a detailed 36 
page manual. 

THE DETECTOR — features Analytical Discrimination 

& Ground Exclusion, backed by the proven pedigree of 
C-Scope, Europe's leading detector manufacturer. 


Ask at your local Hobby/Electronics shop or contact:— 


c ¢ C-Scope International Ltd., Dept. PE 
C (r © Wotton Road, Ashford, Kent TN23 2LN. 


Telephone: 0233 629181. 


SURVEILLANCE 


PROFESSIONAL QUALITY KITS 


A range of high quality kits as supplied to leading UK security companies, all in-house 
designed and produced, not to be confused with cheap imports. All kits come fully 
documented with concise assembly and setting-up details, fibreglass PCB and all 
components. All transmitters are fully tuneable and can be monitored on a normal VHF 
radio or tuned higher for greater security. All units available ready built if required. 





MTX Micro Miniature audio transmitter. 

17mm x 17mm. OV operation. 1000M range. .......ccccecceccesessessecsessessesesssessesessesseeseerseesees £10.95 
VT500 Hi-power audio transmitter. 

250mW output. 20mm x 40mm. 9-12V operation. 2-3000m range 

VOX75 Voice activated transmitter. 

Variable sensitivity. 30mm x 40mm. 9V operation. 1000m range 

CTX900 Sub-carrier scrambled audio transmitter. Cannot be monitored 

without decoder fitted to radio. 30mm x 40mm. 9V operation. 1000m range 

DSX900 Sub-carrier decoder unit for monitoring CTX900. Connects to radio 

earphone socket. Provides output for headphones.35mm x 50mm. 9-12V operation ......£17.95 
HVX400 Mains powered audio transmitter. 

Connects directly to 240V AC supply. 30mm x 35mm. 500m range . .........seccssseecsseeeeee £15.95 
XT89 Crystal controlled audio transmitter. 

High performance. 100mW output. Supplied with xtal for 108MHz. Others 

available to 116MHz. 85mm x 28mm. 9V operation. 2-3000m range 

TKX900 Tracker/Bleeper transmitter. 

Transmits continuous stream of audio pulses. Variable tone and rate. 

Powerful 200mW output. 63mm x 25mm. 9V operation. 2-3000m range. ........e..sssssee. £18.95 
ATR2 Micro size telephone recording interface. Connects between telephone 

line (anywhere) and cassette recorder. Tape switches automatically with 

use of phone. All conversations recorded.Powered from line. 10mm x 35mm 

TLX700 Micro Miniature telephone transmitter. Connects to line (anywhere) 

switches on and off with phone use. All conversations transmitted. 

20mm x 20mm. Powered from line. 1000m range 

XML900 RF bug detector. Variable sensitivity. Triggers LED and bleeper when 

in presence of RF field. Detects MTX 15-20 feet. 55mm x 55mm. 9V operation £21.95 
XL7000 Professional bug detector/locator. Variable sensitivy. Twin mode ten segment LED 
readout of signal strength with variable rate bleeper. Second mode AUDIO CONFIRM 
distinguishes between localised bug transmission and normal legitimate signal such as 
pagers, cellular etc. 70mm x 100MM. OV operation. .......c..cccccccesssecsessessessesssesecsessessecseees £49.95 


UK customers please send cheques, PO's or registered cash. Please add £1.50 per order 
for P&P. Goods despatched ASAP allowing for cheque clearance. Overseas customers 
send sterling bank draft or Eurocheque and add £5.00 per order for shipment. Credit card 
orders accepted on 0827 714476. Full catalogue available on receipt of 28p stamp. Trade 
enquiries welcome. 


THE WORKSHOPS i 
95 MAIN ROAD. BAXTERLEY “——4tf 033: 
Nr Atherstone. WARKS CV9 2LE ES ! 





PRACTICAL ELECTRONICS AUGUST 1989 











Daron \\(@)B) ate 


he Data Encryption Standard allows 
for operation in four different 
modes: 

a) Electronic Code Book (ECB) which is 
a simple encipherment on a block by block 
basis, sometimes called the ‘native’ mode 
since it is so fundamental. 

b) Cipher Block Chaining (CBC) where 
the algorithm is used to scramble the blocks 
together. 

c) Cipher Feedback (CFB) which 
enciphers a string of characters dealing with 
each character as it appears, as from a 
teleprinter. This is a type of stream cipher. 

d) Output Feedback (OFB) which is 
another type of stream cipher. 

Since electronic code book is the 
simplest, in 64 bit blocks, repeating a block 
would reveal useful information to an 
eavesdropper. For instance computer 
messages often repeat and worse still they 
are in a very standard formats with 
messages and headers always in the same 
place. 

In addition, protocol designers usually 
leave large blank spaces so that various 





Corruption must 
be combatted 
at all levels, 
whether due to 
electronic 
instability, or 
criminal wilfulness 





64 BIT STORE 


chains characters and is often known as "m- 
bit" cipher feedback where m is any number 
between | and 64. 

In older message transmission systems 5 
or 6 bit character codes were common, but 
present day systems use 7 or 8 character 
codes. The ISO (International Standardis- 
ation Organisation) 8 bit (octet) is a popular 
method. This comprises 7 information bits 
and | parity bit. 

Fig.17 shows how the octets are added 
module 2 (XOR) to the output of the DES 
algorithm. For an on line system of this 
nature, each octet must be enciphered 
immediately by the transmitter and 
deciphered as soon as it is received by the 
receiver. CFB suffers the same problems of 
error extension as CBC does. 





Fig.14. Cipher block chaining. 


64 BIT STORE 


| 
ENCIPHERED 








ENCRYPTION 








facilities can be incorporated if required for 
a customer. If some of these facilities are 
not required, the spaces are left blank or 
filled with constants. 

Therefore, ECB is not advisable for 
transmitting more than one block and a 
simple application is for transmitting a key 
since a key contains 56 bits of random 
digits. Short messages like acknowledge- 
ments can also be sent in the ECB mode but 
they must be padded out to 64 bits 
otherwise the contents may be obvious. 

The padding can be carried out by 
including a serial number or stamping. the 
acknowledgment with the date and time. 
The date and time occupy 48 bits, so there 
is still room for 16 bits of data. 

In cipher block chaining, Fig.14, each 
block before encoding, is added to the 
cipher of the previous block. This makes 
the nth enciphered block Cn a function of 
the previous plain message blocks M; M) 
M3...Mp. 

The problem is that for the first block, 
there is no ‘previous block' so an initialising 
variable (IV) is sent but the IV must be 
random, otherwise an eavesdropper can 
analyse it. 

One big disadvantage of CBC is that 
errors in one block are extended into other 
blocks because of the chaining. This is 
called error extension and in the case of 
speech, produces clicks or in the case of 
pictures, produces spots. Since speech and 
pictures have redundancy (excess 


PRACTICAL ELECTRONICS AUGUST 1989 


PART TWO 
BY MIKE SANDERS 


information) error extension is only just a 
nuisance, but in data transmission, the data 
could be corrupted excessively. 

In order to prevent data corruption, error 
checks must be carried out and this must be 
carried out directly on the enciphered bit 
stream, Fig.15, not on the plaintext 
message, Fig.16. 

Cipher feedback, Fig.17, is employed 
for chaining when the message is operated 
on in bits or characters. But instead of 
chaining whole blocks, cipher feedback 


Output feedback (OFB), Fig.18, 1s 
similar to CFB except in the manner in 
which the feedback is obtained. But there is 
no chaining and therefore no_ error 
extension, so output feedback is used where 
CBC and CFB would be unacceptable. 
Since an error in the enciphered text is 
directly related to only one particular point 
in the plaintext message, OFB is similar to 
the Vernam cipher. 

OFB uses a pseudo random number 
generator at each end, and these must by 
synchronised. Therefore, if characters are 
gained or lost, OFB~ will lose 
synchronisation, whereas CFB will not. 





Fig.15. (upper) Error check on enciphered message. 
Fig.16. (lower) Error check on plain text message. 


ERROR 
CHECK 


ENCIPHER 


MESSAGE 


es 


DECIPHER 
MESSAGE 


ERROR 
CHECK 





AGAIN 
REQUEST 


ENCIPHERED 


DECIPHER 





SEND 


AGAIN 
REQUEST 


MESSAGE MESSAGE 


MESSAGE 
DATA 


ENCIPHER 
SEND MESSAGE 


AGAIN 
REQUEST 


DECIPHER 
MESSAGE 


39 




















SHIFT REGISTER 


64 
Eee eeEE 
Sane ETRE 
64 


SELECT 8 BITS 
TO THE LEFT 


PLAIN 
MESSAGE (2) 
8 BITS 


| 
| 
| 
| 
| 
| 
| 8 
| 
| 
| 
| 
| 


ENCIPHERED 
ee 


ENCIPHER | 





Fig.17. Cipher feedback 





If OFB loses synchronisation, the 
synchronisation process must be restarted 
by placing a new initialising variable (IV) 
in the shift registers. The IV does not have 
to be encrypted since it does to reveal the 
pseudo-random stream if intercepted by an 
eavesdropper. 

The pseudo random stream is not a truly 
random number like that generated from a 
noise source but an artificially generated 
one using shift registers and XOR functions 
hence the name pseudo-random. 

The pseudo random stream must not 
repeat. If it does then an eavesdropper can 
easily eliminate it by a simultaneous 
equation as follows: 

Let X be the pseudo random stream 

Let M be one plaintext message 

Let N be another plaintext message 

Then the first enciphered message 

is X +M 

The second enciphered message is X + N 

To eliminate X these two enciphered 
messages are added module 2 giving M+ N 
which is the same as enciphering M with N. 
The pseudo-random stream is also called 
the key stream. 


DES HARDWARE 


The transpositions required in present 
day ciphers are difficult to implement in 
terms of hardware. A small telephone 
exchange would be required to implement 
all the permutations of an algorithm. An 
alternative is to write a computer program, 
but this is slow and therefore inefficient. 
Therefore, the state of the art at present is to 
use hybrid methods employing operations 
like shift, add and XOR acting on whole 
words. 

There are several manufacturers of DES 
chips. The Burroughs MC 884 is an n- 
channel ttl compatible chip employing 
silicon gates. The clock speed is from 
0.SMHz to 1.25MHz and there are 32 
different clock speeds which are required 
by the algorithm. A second Isi chip MC883 
is required to control the MC884 and 
encryption or decryption takes 25us to 
64us. 


40 


SHIFT REGISTER 


SELECT 8 BITS 
TO THE LEFT 


DECIPHER 


64 


64 


m 


m BITS 
PLAIN (2) 
MESSAGE 


6-2) PLAIN 
MESSAGE 
8 BITS 


SHIFT REGISTER 


64 
EReERR 
A _, — J 


SELECT m BITS 
TO THE LEFT 


ENCIPHER 


SHIFT REGISTER ‘i 
pL Tt tt TY 
YY 


64 


| 
| 
| 
| 
| 
| 64 
| 
| 
| 
| 


SELECT m BITS 
TO THE LEFT 


m 


m BITS 


m BIT G2) 
ENCIPHERED MESSAGE PLAIN 
MESSAGE 


| 
| DECIPHER 





Fig.18. Output feedback 


Motorola makes the MC6859 with a 
2MHz clock and an encryption time of 
10us. Western Digital makes the 3 chip set 
WD 2001E/F, WD 2002A/B, WD 2003 


using n-channel silicon gates. And 
advanced Micro Devices makes the 
AmZ8068. 


The DES algorithm can also be 
implemented in microprocessor form. The 
Intel 8294 uses a microcode stored on a 
prom (programmable read only memory). 
American Microsystems makes the S6894 
which is a 2 chip microprocessor, and Texas 
Instruments makes the TMS 9940 with a 
SMHz clock. Rockwell Collins and 
Motorola supply circuit boards for 
interfaces and key management. 


PUBLIC KEY CIPHERS 


In a symmetric cipher, the key is secret 
and is known only to the communicating 
parties. In an asymmetric cipher the sender 
has his own key and the receiver has his 
own. The latter are called public key 
ciphers and were developed by Diffe and 
Hellman in 1976. 

Fig.19. shows how a public key cipher 
works. For enciphering the message, key e 
and the algorithm E is used and to decipher 
the message, key d and algorithm D is used. 
A seed or starting key s is used to derive 
keys e and d using algorithms F and G. The 
algorithms D, E, F, G are all public 
knowledge since anyone can buy the 
encryption boxes and study them anyway. 





Fig.19. Public cipher key. 


RECEIVER 
GENERATES 


0161339 








In order for the recipient to be the only 
one to decipher the message, he must be the 
one to derive both keys e and d using 
algorithms F and G. He then announces key 
e and keeps key d secret. The first 
publications did not detail the algorithms D, 
E, F and G to produce a working model. 

It was left to Rivest, Shamir and 
Adleman in 1978 to produce the first 
working model and it is now the well 
known RSA method. F is known as a one 
way function since knowledge of the key e 
must not enable an unauthorised person to 
calculate keys s and d. E is also a one way 
function since knowing the ciphertext y 
should not enable calculation of the 
plaintext x. 

Since e is now a_ public key, 
authentication is not provided since there is 
no point in proving that the sender is 
geniune. 

The two key public method can be 
illustrated as follows. With reference to 
Fig.20a, suppose company A wants to send 
company B a message in a case without 
sending the key. They apply padlock A to 
the case and send it with a courier, without 
sending the key. When it gets to B Fig.20b 


Fig.20. Illustrating 2-key ciphers 


SENDER A SENDER B 


LOCK A LOCK B 
SENDER A 


SENDER B- 


(> LOCK B 


last 


SENDER A 


SENDER B 


SENDER A 
[0161340] 


SENDER B 


PRACTICAL ELECTRONICS AUGUST 1989 








company B also apply their padlock and 
return the case to company A, who remove 


their padlock Fig.20c. The case then travels - 


to company B who remove their padlock B, 
Fig.20d, and read the message. 

It may seem longwinded but when it is 
remembered that data travels up and down a 
communications link quite quickly, it is no 
problem to transfer it back and forth for the 
sake of security. 

The RSA method is based simply on a 
number which is a product of two very 
large prime numbers. Suppose this product 
is m = xy, the recipient is the one who 
chooses x and y and then announces the 
number m which will be used as part of the 
public key. 

Of course, m is of no use if it can be 
easily factorised and if m is small, it can be 
easily factorised. On the other hand if m is 
large, the factors are difficult to find. This is 
a well known problem in mathematics so it 
has been given considerable thought. 


LEKTOR 


In the Lektor system developed by 
British Telecommunications, the large 
prime numbers x and y are up to 128 bits in 
length. The number m is then up to 256 bits 
in length and is called the modulus. The 
numbers x and y are called relative prime, 
ie they cannot be factorised and _ their 
divisors are only themselves and one. 

Since the public key cipher method is 
slow it is usually used only to distribute the 
session key. The parties can then revert to a 
faster real time transfer of data like B-Crypt 
also developed by British Telecommuni- 
cations. In addition, Lektor has facilities for 
using DES for those who prefer DES. 

Lektor employs user tokens in the form 
of a physical key and pin numbers as used 
by cash tills. Lektor can also be used to 
encode facsimile (still picture) transmission. 


KEY MANAGEMENT 


The distribution of keys and the control 
of keys is an art in itself since the security 
of a modern system depends not on the 
algorithm but on the keys remaining secret. 

If s is a key used to encipher data for 
only one session it is called a session key. 
In order to send the key through the 
network, it is enciphered with another key t 
called a terminal key. Key t is used more 
often than key s so it is stored at the host 
computer under the care of a master key. 

In order to generate the master key, a 
very mundane method is used. A dice is 
rolled or a coin is tossed in order to select 
each digit. This may seem a_ labour 
intensive method of generating a random 
number but it is reliable and in any case, a 
master key is not changed often. 

In order to generate keys below the 
_ master key level a pseudo random number 





PRACTICAL ELECTRONICS AUGUST 1989 





generator or a random bit generator is 
employed. The latter could use a resistor as 
a noise source and a wideband amplifier for 
switching a gate on and off. Zero crossings 
of the signal are used and the output is 
sampled to give a | or 0 at fixed intervals. 

Terminal keys can also be distributed by 
a courier and a key module the size of a 
pocket calculator. The module is plugged 
into the host computer and the key is 
loaded. Actually loading the keys into the 
destination computer must be carried out in 
the presence of reliable personnel. 

The module presents a number of 
problems. An unreliable courier could copy 
a key or insert a false key. Copying the key 
can be defeated by arranging that reading 
the key erases the key from the module 
memory. Therefore is say three terminals 
require the same key, this key must be 
loaded three times into the module. 

Installing a false key can be overcome 
by the use of a password, and it could be 
arranged such that say more than three 
attempts at guessing the password, activates 
the module so that the keys are erased. 


AUTHENTICATION 


It is interesting to note that enciphering 
data only prevents an enemy from adding 
new data. But there are other forms of 
active attack like: 

a) deleting blocks of data 

b) altering the sequence of blocks 

c) repeating previous blocks 

d) altering the destination 

e) falsifying an acknowledgement 

f) making the recipient think that 

the data originated at a location 

other than its true origin 

So a fair bit of mischief can be 
perpetrated without actually breaking all of 
the code. 

The need for authentication may well be 
questioned when one is using a secret key. 
However, there are many instances when 
encipherment may be inconvenient and the 
parties may rely on __ occasional 
authentication checks only. 

For instances point to multipoint 
broadcast may be in progress as from a 
taxicab base station to all its mobile units. 
This may be in plain English for 
convenience with only one _ receiver 
checking the authentication digit fields to 
ensure someone is not sending out false 
messages. 

Another instance may be a computer 
with a heavy work load. Here time wasted 
in deciphering every step of a program 
could be spent in running the program 
itself. Therefore, cipher security may be 
exchanged for an authentication field so 
that the computer can carry out a quick 
check and assure the programmer that all is 
well. 

In the cipher block chaining mode of the 
DES, the authenticator is calculated from 
the final output block by taking the most 


= ENCRYPTION: 


‘ate’ 


Yi, Sis. SOON 
“th SQ 
> * 





significant m bits. In the USA, the 
authenticator is called the Message 
Authentication code (MAC) or the Data 
Authentication Code (DAC). 

For financial transactions it is 
recommended that the MAC be greater than 
32 bits long and for telecommunications, 
the MAC should be greater than 24 bits. 
Authentication protects the communicating 
parties against a third party but not against 
each other. For protection against each 
other, the parties require digital signatures, 
which will be dealt with later. 


IDENTIFICATION 


Identification is an essential part of data 
security. This is achieved by many methods 
some of which are more suitable than others 
for electronic scanning. Passwords for 
accessing computers and pin numbers for 
accessing cash bills are two such methods. 

Personal characteristics which are highly 
individual can also be used for electronic 
scanning but are usually unacceptable for 
one reason or another. Such characteristics 
include finger prints, the voice, retinal 
patterns and the handwritten signature. 

Passwords are of several kinds: 

(i) The most common are those that 

are unique for each person. 

(ii) Those that are not unique but 

aid identification, eg pin numbers. 

(iii) Passwords that are known to 

a group of people. 

(iv) Passwords which are used 

only once. 

When a computer terminal fails to 
recognise a genuine person, this is called a 
Type I error, and when it gives access to a 
false individual, keying in the wrong code, 
this is called a Type II error. 

If people were permitted to choose their 
own passwords, the most common choices 
would be: 

a) words spelt backwards 

b) car numbers, telephone numbers 

and social security numbers 

c) town names and street names 

d) surnames and first names 

A recent survey showed that about 85% 
of passwords could be cracked because they 
fell into one of these simple categories 
when people chose their own passwords. 

The most common form of identification 
on paper documents is by a Signature. 
Forgeries are of three kinds: improvised, 
copied and traced. An improvised one 
happens when someone finds a cheque, and 
because the owner's name is now printed on 
each cheque, the finder makes a guess at 
what the signature might look like. This 
may fool a shopkeeper but not the owner's 
bank. 

A copied signature is one where the 
forger has a copy of the owner's signature 
and after a few practice attempts, has a go 
at signing a cheque. A traced signature is 
the hardest to detect but for the copied 
signature, Nagel and Reosenfeld have 





41 








invented a machine which compares the 
angles of slant and dimension ratios with a 
specimen of the true signature. 

A signature verification system called 
VERISIGN has also been developed by the 
National Physical Laboratory. This uses a 
pad called CHIT and is made from two 
membranes which touch when the pen is 
pressed down on the surface. The x and y 
co-ordinates of the signature are then 
plotted by sampling at the rate of 50 times 
per second. 

Ten different characteristics are assessed 
such as velocity and acceleration, turns, 
slopes and loops and the number of 
contacts. The time taken for an individual to 
sign his name varies very little and this in 
itself is a good check. 

A voice verification system has been 
developed by Texas Instruments. The 
candidate is required to utter 16 words 
containing vowels and from this the 
machine produces 32 sentences. By 
sampling at 10ms intervals, a Fourier 
analysis detects the large amplitude regions 
and bands are selected in the range 300Hz 
to 250Hz. The information is stored and 
compared with samples from later visits. 
However, a cold or stress changes the voice 
and even asking the candidate to repeat 
words could lead to stress. 

Finger prints are also highly individual. 
These are based on the loop, whorl and 
arch, Fig.21, and finger printing has 
developed by Sir Edward Henry in 1897, 
the Metropolitan Commissioner of Police. 


Fig.21. Loop, whirl and arch. 





Unfortunately, fingerprints are 
connected with crime and the public is not 
likely to embrace such a system, even 
though an ink-pad is not involved. The 
person requesting access has merely to 
place his fingers on a sheet of glass, and a 
light from underneath reflects off the 
fingertips. 

The retinal pattern is also unique to 
individuals and provides another means of 
identification. Eyedentify of Oregon have 
invented an infra-red scanner which detects 
the pattern of blood vessels on the retina 
when one looks into the binocular eyepiece. 
The nodes and branches within the scanned 
area is then registered. 


42 


EMBOSSED INFORMATION 


NEAREST EDGE 


eee ae a a 3 
8:46-8:97 
8:46 - 8:97 
\11-76- 12:27 
ig 1201-12-52 
, 15-32 - 15-82 


TRACK 1) * 


MAGNETIC 


STRIPE  _TRACK 2 


TRACK 3 


ATMS AND PINS 


Automatic Teller Machines (atm) are 
used to describe cash tills which do a bit 
more than just dispense cash. They also 
provide statements of the account and 
transfer between accounts. ATMs are of two 
kinds, on line and off line. 

Off line atms are easier to fool since 
they are not updated till the next cycle, 
usually around midnight. Therefore, a 
stolen or forged card can be used many 
times. On the other hand an on-line terminal 
can detect excessive activity, either by the 
number of withdrawals or if the amount 
permitted has been exceeded. 

The usual token for accessing an atm is 
a plastic card and pin number. The 
International Organisation for 
Standardisation (ISO) has defined the 
dimensions of this card, Fig.22, as well as 
the tracks on the magnetic stripe. The stripe 
itself can be "watermarked" to prevent 
forgery. 

The Emidata/Malco system arranges for 
magnetic stripes angled at 45 degrees 
alternately, by means of a recording head. 
The stripe also carries between 50 and 100 
bits of data. Given all this security it is little 
wonder that unscrupulous people prefer to 
steal a card and pin number rather than 
attempt to forge a card and pin number. A 
survey showed that an average US 
businessman carries something like 11 
cards so it is not easy to memorise all the 
pin numbers. 





1036 1343] 1343 


(0:76mm THICK) 


Fig.22. ATM 
and stripe. 
Inset above 
shows 
magnetic 
watermark. 





The standards for pin management 
expect organisations to use pin numbers 
between 4 and 12 digits long. In practice, 
typical pin numbers are 4, 5 or 6 digits long 
perhaps to assist people to remember them 
without writing them down. 

A pin number can be derived from an 
account number as shown in Fig.23. Using 
zeros or constants, the account number is 
padded out to 16 decimal digits. The 64 bit 
number produced is then enciphered using 
DES and a secret key and the 64 bit output 
is examined in groups of 4 bits starting at 
the least significant bit end. Those groups 
whose decimal equivalent is less than 10 
are accepted and the required M digit pin 
number is obtained. In practice a slight 
adjustment is made if too many or too few 
decimal digits have been produced. 

PIN numbers are typed by printers 
without ribbons so that an unscrupulous 
person cannot steal the ribbon and read it 
afterwards, hence security is improved. 
Instead a carbon type of paper which is 
already inside a sealed envelope is inserted 
into the printer and this envelope is posted 
separately from the plastic card. 

Another method of choosing a pin 
number could be by a visit to the bank 
where customers would have the facility of 
typing their chosen number onto a computer 
terminal. Although the local bank staff may 
not see the pin number, it could be assessed 
by the systems operators. 

A recent development is the so called 
smart card which is active and can, 
therefore, handle a certain amount of 





Fig.23. PIN number from account number. 


PADDED 
ACCOUNT TO 


16 DECIMAL 
DIGITS 





M DECIMAL PIN 
DIGITS NUMBER 


[0161344] 


PRACTICAL ELECTRONICS AUGUST 1989 








processing. (Smart cards were discussed in 
Home Automation, PE May ‘89. Ed) Its 
storage is 250 bytes compared to the 100 
bits of the ordinary card. The information 
can be stored in a hologram and is used for 
such things as paying for phone calls and 
transport and viewing television, and the 
number of credit units held in the hologram 
is decremented each time it is used. The 
active card did not appear earlier because 
the requirements were to maintain the 
durability and dimensions of the previous 
card, therefore, fragile chips would have 
been unsuitable. Nevertheless cards with 
chips are also in use as well as cards with 
magnetic stores. 


oy OO) NI (Ou O INI Dio 


The Society of Worldwide Interbank 
Financial Telecommunications (SWIFT) 
was set up to speed international payments. 
It is a non-profit bank owned by 1000 
shareholding banks in 50 _ countries. 
Passwords are used only once and tables of 
passwords are despatched in two halves so 
that if one half is intercepted, no harm is 
done. 

There is no point in developing an 
international system if a national system 
does not exist to aid and support the 
international system. For this purpose the 
Clearing House Interbank Payment System 
(CHIPS) was established in the USA and 
Clearing Houses Automated Payment 
System (CHAPS) in the UK. 

DES in the CBC mode is_ the 
authenticator used in CHAPS, and CHAPS 
operates over the part of the public 
telephone network called packet 
switchstream (PSS). The interface of 
CHAPS software with the banks software is 
called the gateway, Fig.25. The gateways 
must be reliable and the PSS network must 
have a high availability. 


GATEWAY 


BANK'S CHAPS 


SOFTWARE ; SOFTWARE 


PAY IN 
SYSTEM 


AUTHENTICATOR 


Fig.25. CHAPS operation 


In the PSS network, data is chopped into 
fixed lengths and transmitted between 
nodes when the link is free as opposed to a 
dedicated link in a telephone network which 
carries traffic between those terminals for 
the duration of the call. 

Each originating gateway receives an 
acknowledgement for each message sent. 
The gateways also apply time stamps and 
sequence numbers and keep a running total 
of the money. Therefore, not only is the link 
performance monitored at all times, the 
finances are also kept up to date. 


PRACTICAL ELECTRONICS AUGUST 1989 





Both these aspects are essential since 
CHAPS offers same day settlement of 
accounts which is vital to those who are 
moving house for instance. On the final 
date called ‘completion’ the seller wants to 
be sure of receiving the money since he is 
also vacating the house. Thirteen settlement 
banks in London are linked into CHAPS 
and about 300 banks in the UK including 
foreign banks. 





DCN Ere CIN AUC lalate 


On paper documents, a signature has 
always been the ultimate authority. In 
electronic communications, authentication 
is useful against third parties, but does not 
provide security between the 
communicating parties. 

Both sender and receiver have scope for 
cheating in the absence of a digital 
signature. For instance the sender could 
deny instructions to his broker if the shares 
suddenly look unfavourable. A_ receiver 
could cheat by altering the amounts and 
frequency of payment to himself. 

A digital signature is a number which 
depends on all the bits of the message and 
also on the secret key. A digital signature 
can be checked by means of a public key 
whereas an authenticator requires a secret 
key. 

A public communications system 
provides either authentication or secrecy 
and if both must be combined then 
signature methods as well as encipherment 
must be used. 

A symmetric cipher can also be used for 
digital signature but an arbitrator must be 
employed. The arbitration service is called 
the ‘authentication server’ by Needham and 
Schroeder and is probably better suited to 
internal communications in a large firm. 

The arbitrator must be trusted by all 


GATEWAY 
PACKET 
SWITCHED 
NETWORK 
(PSS) 


AUTHENTICATOR 


BANK'S CHAPS 
SOFTWARE ! SOFTWARE 


PAY IN 
SYSTEM 


parties to time and date stamp all messages. 
A random number or serial number in the 
transmission is also checked to ensure no 
one interferes with the message. 

If the sender has lost his key or believes 
it has been stolen, he can recall all his 
messages. This may give rise to a fraud 
dispute but it is no worse than any other 
fraud dispute. If a sender is careless enough 
to lose his keys, he is likely to lose business 
and if he only pretends to lose his key, he is 
also likely to lose business. 


So he can hardly continue _ the 








ENCRYPTION® 





masquerade particularly if he stands to gain 
by pretending to lose his key. In general 
digital signatures are more reliable than 
handwritten signatures, since they are 
automatically checked whereas handwritten 
signatures are accepted at face value. 
Therefore, digital signatures help automate 
business processes. 

Enciphering used to require human skill 
and intuition and was an art. Now, 
computing can break the classical methods 
by brute force, first to identify the type of 
cipher and then to break into the 
combinations. In addition to finding the key 
and cracking the algorithm, the modulation 
of the transmission system and the plaintext 
language must also be found. 


CIPHER SI RAENt Im 


In estimating the strength of a cipher if 
the cryptanalyst does not have any idea of 
the plaintext and has only the ciphertext to 
work on, this is called a ciphertext only 
attack. It is impossible to find the key if the 
message is very short and _ without 
redundancy. 

If there is redundancy like an arbitrary 
string of constants or known preamble as in 
computer or satellite communications then 
cryptanalysis becomes easier. This is called 
the known plaintext attack, and is possible 
in more situations than one would expect. 

For instance political unrest would lead 
to a message from an embassy to its home 
country and spectacular changes on the 
stockmarket would cause a high activity of 
messages between banks and stockbrokers. 

A bombing run on a lightbuoy during 
World War II led to the word leuchttonne 
appearing in Enigma messages. This was 
predictable and is called the chosen plaintext 
attack. If the attacker is crafty enough he can 
use his agents to slip his own words into his 
enemy for encipherment and this in another 
case of a chosen plaintext attack. 

In modern ciphers the key and not the 
algorithm is the all important item. Suppose 
lsi hardware is used to search for the key 
and that the key is found after exploring 
only half the key space, Table 1 shows the 
time taken to search keys of varying size. 

Table 1 also shows a machine beyond 
our present technology capable of doing a 
million tests in parallel and searching 
separate parts of the key space. Whereas the 
lsi is capable of lus per test, the imaginary 
machine does a million tests in the same 
time and even a 64 bit key becomes 
insecure. 


AB | 


One million 
tests in parallel 
1 ps per test 


Key Size Single Tests 


1 Us per test 
32 35 minutes 2.15ms 
48 4.46 years 2:35 minutes 
64 107 days 


43 








Shannon put security in two classes: 
unconditionally secure and computationally 
secure. One time tapes with random keys or 
very short messages contained in a key are 
unconditionally secure since no amount of 
computing power can break them. 

Those ciphers which are 
computationally secure are those which 
cannot be broken by today's computing 
power but may be broken in the future. If a 
step is defined as the work that lsi hardware 
can carry out in lus, then today's technology 
cannot cope with more than 10” steps. 

Certainly, time can be cut down by large 
money stores and parallel processing, and 
these will be used increasingly in the future. 
To be on the safe side, assessment of cipher 
Strength must assume conditions which 
favour the enemy like a chosen plaintext or 
known plaintext. 

Shannon defined the ‘unicity distances’ 
as the minimum length of text which will 
provide a unique solution. That is, the 
redundancy in the plaintext must be greater 
than the information in the key. 

Taking monoalphabetic ciphers as an 
example, the key size is 26! and log2 26! is 
88. Assuming that English is 80% 
redundant, each character provides 3.8 bits 
of redundancy. Hence a cipher with 88/3.8 
or about 23 characters is the unicity 
distance. 

Therefore, a text with more than 23 
characters will contain redundnacy. 
Shannon's calculations take into account 
text with spaces, therefore, text without 
spaces will need a bit for monoalphabetic 
substitution. 

The DES algorithm can be strengthened 
by increasing the key space, but then the 
hardware would be more expensive. In a 
good algorithm the output is not linearly 
related to the input and changing, even one 
bit in the key would produce a bit change in 
the output. 

Various estimates have been produced 
for the cost-time trade off of a machine 
capable of carrying out a search for a DES 
key. Cost estimates ranged from 20 to 200 


soemmanune, Ss, 


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CRO reya\ane 


Autobank Teller Machine 
Cipher Block Chaining 

Cipher Feedback 

Clearing House Interbank 
Payment System 

Clearing Houses Automated 
Payment System 

Data Authentication Code 
Data Encryption Standard 
Electronic Code Book 
International Standardisation 
Organisation 

Initialising Variable 

Message Authentication Code 
National Bureau of Standards 
Output Feedback 

Packet Switchstream 

Society of Worldwide Interbank 
Financial Telecommunications 


million dollars an the time from 20 hours to 
11,000 years. But it is not worth the time or 
effort since DES ~ machines carry 
commercial, unclassified information. 

To meet the challenge of improving 
technology the permutations, S boxes and 
keying methods can be improved in 
addition to changing the key size, data 
blocks and sub key generators. 

Conducting an exhaustive key search on 
the 128 bit Lucifer system would take 1019 
years, assuming one key is tested per 
picosecond, since there are 3 x 10°° keys. 

Ultimately, both a thermodynamic limit 
as well as a limit on the storage must defeat 
an exhaustive key search. Suppose each step 
requires energy KT where K is Boltzman's 
constant and T is the absolute temperature. 
Assuming that the calculations will take 
place at 100°k and from calculations of the 
sun's rays heating the earth, 3 x 1048 
calculations will take 1000 years. 

The other important requirement is 
memory space. Assuming one binary digit 
needs only 10 atoms of silicon, 10 5 bits 


will cover all the dry land to a height of 
lkm. Alternatively a satellite of similar 
mass will have to be put in orbit. 

When machines become too expensive 
for code breaking, more mundane methods 
will be adopted like merely stealing a card 
and pin or bribing a person in a position of 
trust. 


CONGRESS ICING 


Early ciphers depended on substitutions 
and transpositions, but when the two are 
combined, machines are required otherwise 
humans would be too slow and inaccurate. 

The DES was described as an example 
of a modern cipher where the emphasis has 
changed from secrecy of the algorithm to 
secrecy of the key. With this change in 
emphasis, key management then becomes 
an art in itself. 

Together with public key ciphers, other 
improvements have been introduced such as 
identification, authentication and digital 
signatures, all of which are essential for 
automating business using atms and 
CHAPS. 

The security of a cipher is never guaran- 
teed and hackers, when they are caught, do 
not have the same guilt feelings as those 
who steal money. Society probably looks on 
them with mild amusement and curiosity. 
However, damage of a varying extent can 
be caused by unauthorised people accessing 
medical records, financial records and 
military networks. 


BIBLIOGRAPHY 


How Encryption Secures Data, H. 
Pollock, Can. Datasyst Vol. 19. 
Cryptanalysis, H.F.-Gaines. 
Security from Attack, R. Gibbs, Comm. 
Int (GB) Vol. 14. 


The Code Breakers, D. Kahn 


TRAINING 


HNC in Microprocessor Systems 
A one year full time course, commencing on 4th September 
1989, is offered by Milton Keynes Skillcentre. 


The course includes 20 weeks work placement in Industry. 
This is a Traning Agency funded equal opportunity course 
and training allowances will be paid. 

Please phone 0908 670001 for an application form or write to: 


Chesney Wold, 
Bleak Hall, 
Milton Keynes, 


Fax: 01-807 2748 Tel: 01-803 6068 


44 


MSO ee 


Milton Keynes Skillcentre, 


Pi 


Skills Training Agency 





PRACTICAL ELECTRONICS AUGUST 1989 











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In direct mode the bar-graph readout will detect the presence of negative or 
positive ions and measure neg-ion strengths from 5 x 10” to 10°° ions per 
second, which covers the levels you can expect when an air ioniser isin use. 
For the smaller concentrations of natural airions, integrate mode will increase 
the sensitivity as far as you like. 

Our approved parts set comprises: case, ion collector, printed circuit board, 
all components (including six ICs, schottky diode, cermets, VDR, zener, 

37 resistors and capacitors, LEDs, plug, socket, earth lead, etc.) 


13) 5 
) ions every minute, or 


1S per second, 
With extra emitters this can be 
Increased stil further! 


PARTS 
SET £24.80 yer 





ea full instructions. - 5 The parts set and ful me 

‘ iCIUdES Case, printed PARTS SET £16.40 + VAT 

Ben Sweetland’s best seller GROW RICH WHILE YOU SLEEP Circuit boards, 126 top pt vipa eigermc ripen anlage sgn pothesis a 
isnowin stock. £2.95 (NovAT) SAE + £1 for lists, circuit, construction details and further information (free 


grade components 
controls, lamps, hardware : 
multi-point phospher-bronze 


with parts set). 





emitter and full instructions, BIO 
TV BOOSTER se are available separately — 
Send SAE for lists C aS 
Good TV pictures from poor + £1 for lists, Circuit and site SAE FEED B A K = 
aerials is what this projects al details and further ruction eel 
about. Keith Brindley's Aerial pia r information FEATURED IN ETI 
nua RF A DY. B ul ee with parts set), DECEMBER 1986 
N : 
campers and caravanners, from LT MISTRAL |P ; fa 
indoor aerials, or wherever a The Mistral lonj OAR D Bio-Ieacbacr comes Ol age 
property positioned high-gain ral loniser (and most of with this highly responsive, 
antennas not practical Projects) can now b Our other self-balancing skin 





€ Supplied buil 
and ready to go. For details, fies ae 


contact Peter Leah at PL. Electronics 


response monitor! The 
pow2rful circuit has found application in clinical situations 
as well as on the bio-feedback scene. It will open your 
eyes to what GSR techniques are really all about. 

The complete parts set includes case, PCB, all 
components, leads, electrodes, conductive gel, and full 
instructions. 


CLEANER 


Essential for removin 


flux residues from the Mistral PCB to 


achieve peak perf. 
brush supplied, mimance. Applicator 


ION FAN 


An almost silent pj i 
pieZo-electri 
Operated, to Pump ions away from the 


emitter and into the room. Increases the 


effectiveness of any ioniser by five times! 


Based on the OM335 hybrid amplifier, the booster has specifications to rival 
the best: wideband operation from 10MHZz to 1.4 GHz, mid-band gain of up to 
260B and a wide supply range of 9V to 26V (it will run from car batteries for 
caravanners, dry batteries for campers, or a mains ‘battery eliminator’in the - teres ” Road, Eastville, Bristol BS 56 
home), No special UF construction skills are needed — the project could be el: 0272 5227 TT. 


made by a careful beginner. | NT ‘ 

There are two parts sets for the project. AA1 contains the printed circuit board, ERNAL EMI ER 
OM335 hybrid amplifier, components and instructions. AA2 is the optional C : f 
case set: rugged screened box, front and rear panels, waterproofing gaskets, 


feet, sockets and hardware. 


£0.98 + var 


9 grease and 


PARTS SET £15.80 + vat 
BIO-FEEDBACK BOOK £4.50 (no vaT) 


£9.80 yar 


Cfan, mains 


AA1 PARTS SET £12.80 + VAT for the highest ion 0 


includes PCB 


RTS SET £4.80 + VAT l 
AA2 PARTS SET E + and instructions. 


Please note: the book, by Stern and Ray, is an authorised guide to 
the potential of bio-feedback techniques. It is not a hobby book, 


and will only be of interest to intelligent adults. 





IONISER Be safe from intruders with our Burglar Buster alarm system! It has all the | r @ 
features you'd expect from a high-tech alarm: entry and exit delay, ~ 
FEATURED IN ETI anti-tamper loop, delay waming and control-box protection. Green rectangular LEDs 
JULY 1986 for bar-graph displays. 
The parts set includes ail four PCBs and all components to go on them. Other 50 for £3.50 500 for £25 SERRE WET 
lons have been described as parts (case, switches, etc.) are available separately, if you haven't got 100 for £6 1000 for £45 MIGUST 1987 
‘vitamins of the air’ by the anything suitable in your spares box. Set contains 4 PCBs, ICs, transistors, 


relays, capacitors, resistors, diodes, regulator, piezo sounder and full 
instructions. 


DIGITAL AND AUDIO EQUIPMENT LEDs 
Assorted 3mm LEDs: red, green, yellow and orange. 
25 of each (100 LEDs) for £6.80 


health magazines, and have 
been credited with everything 
from curing hay fever and asthma to improving concentration and 
putting an end to insomnia. Although some of the claims may be 
exaggerated, there is no doubt that ionised air is much cleaner 
and purer, and seems much more invigorating than ‘dead’ air. 

The DIRECT ION ioniser caused a great deal of excitement when 
it appeared as a constructional project in ETI. At last, an ioniser 
that was comparable with (better than?) commercial products, 
was reliable, good to build. .. and fun! Apart from the serious 
applications, some of the suggested experiments were outrageous! 


The most antonishing project ever to have appeared in an 
electronics magazine. Similar in principle to a medical EEG 
machine, this project allows you to hear the characteristic 
rhythms of your own mind! The alpha, beta and theta forms can 
be selected for study and the three articles give masses of 
information on their interpretation and powers. 

In conjunction with Dr. Lewis's Alpha Plan, the monitor can be 
used to overcome shyness, to help you feel confident in 
stressful situations, and to train yourself to excel at things you're 
‘no good at’. 


BB1 PARTS SET £12.80 + VAT 


U.K. orders: please add 80p post and packing 
and 15% VAT to total. 

Eire and overseas: 

no VAT. Carriage and insurance £4.50. 

Please allow up to 14 days for delivery. 








We can supply a matched set of parts, fully approved by the 

designer, to build this unique project. The set includes a roller 

tinned printed circuit board, 66 components, case, mains lead, 

and even the parts for the tester. According to one customer, the 

set costs ‘about a third of the price of the individual components . 

What more can we say? Instructions 
r 


. e 
PARTS SET WITH BLACK CASE £11.50 + var "“luded 
PARTS SET WITH WHITE CASE £11.80 + VAT 





KCONLDUICUOIRSS 





Tel: (0600) 3715 


LIMITED 


SALES DEPT., ROOM 108 ,FOUNDERS HOUSE, REDBROOK, MONMOUTH, GWENT. 


PRACTICAL ELECTRONICS AUGUST 1989 


Our approved parts set contains case, two PCBs, screening can 
for bio-amplifier, all components (including three PMI precision 
amplifiers), leads, brass electrodes and full instructions. 
PARTS SET £36.90 + VAT ALPHA PLAN BOOK £2.50 
SILVER SOLUTION (tor plating electrodes) £3.60 + VAT 

Parts set available separately. We also have a range of accessories, 
professional electrodes, books, etc. Please send SAE for lists, or 


SAE + £2 for lists, construction details and further information (free with 
parts set). 


45 





adly, we must now give up all hope 
Ss: re-contacting the Russian probe 

Phobos 2, which "went missing" 
soon after it had started to send back useful 
data. Some pictures of Phobos, Mars’ inner 
satellite, were received, though it cannot be 
said that they rivalled those obtained by the 
American Viking probes more than a 
decade ago. However, one experiment 
carried on Phobos 2 does seem to have 
worked. It was master-minded by the Irish 
scientist Dr Susan McKenna-Lawlor, and 
was aimed at detecting charged particles in 
the region of Mars. Preliminary data 
indicates that the results were positive, in 
which case Mars does have Van-Allen type 
belts, albeit weak ones, and probably a 
magnetic field. It is a great pity that contact 
with Phobos 2 was lost at so early a stage. 

There is still considerable doubt about the 
existence of the pulsar in the Large Cloud of 
Magellan, produced by the supernova which 
has caused such excitement. The presence 
of a pulsar was reported by observers at the 
Cerro Tololo Observatory in Chile, but so 
far nobody else has been able to see it, and 
at the moment it must be regarded as 'non 
proven’. There is every likelihood that a 
pulsar has been formed, but we must simply 
wait to see what happens next. 

Also in Chile, the NTT or New 
Technology Telescope at the La Silla 
Observatory has been brought into use, and 
is proving to be every bit as good as had 
been hoped. It is of 'modern' design, with a 





BY DR PATRICK MOORE CBE 


One up, one down... 
Telescopes come 
and go 





thin mirror, and an altazimuth mounting; its 
mirror has active optics, ie, the shape is 
controlled by computers as the mirror is 
moved around, thereby compensating for 
flexure, and although it is not the world's 
largest single-mirror telescope there seems 
every chance that it will prove to be the 
most effective. It has even been claimed 
that it will rival the performance of the 
Hubble Space Telescope which will, we 
hope, be launched early next year. 

On the debit side, it has been established 
that the collapse of the 300-foot radio 
telescope at Green Bank, West Virginia, was 
due solely to metal fatigue. In the words of 
one of the investigators, "it just wore out". 
A replacement is already being planned, but 
will not be built for some years yet. 

At the end of April a sad 'farewell party' 
was held at Herstmonceux Castle to mark 
the end of the Royal Greenwich 
Observatory's career there. The 
Observatory is to be moved to an office 
block at Cambridge, where we can only 
hope that it will manage to retain its 
separate identity. 


THE CASSINI PROBE 


Funds have now been definitely allocated 
for the Cassini Probe, which is to be 
launched toward Saturn. True, it will not 
arrive until early in the next century, but it 








46 


PRACTICAL ELECTRONICS AUGUST 1989 














should prove to be among the most 
informative of the space-craft. 

We know a good deal about Saturn itself, 
but not nearly so much about Titan, its 
senior satellite, which will be Cassini's 
main target. Titan, larger than our Moon 
and almost as large as the planet Mercury, 
has a dense atmosphere which is made up 
chiefly of nitrogen, with a good deal of 
methane. Organic compounds no doubt 
exist, and the main objection to the 
existence of life is the very low 
temperature. 

But has Titan a liquid surface? This may 
well be the case. Of course, the liquid will 
not be of water, but it may be that much of 
the satellite is covered with a methane 
ocean, in which case Cassini's ‘lander’ may 
have to be capable of floating. Whether we 
will be able to find out before the probe is 
launched remains to be seen, but at any rate 
the Titan mission is something to which 
astronomers look forward with considerable 


eagerness! PE 


The photograph shows the New 
Technology Telescope in the workshops 
of INNSE at Brescia, Italy prior to 
being installed at the La_ Scilla 


Observatory in Chile. The photo is 
reproduced by kind permission of 
Astronomy Now to whom it was 
supplied by courtesy of the ESO 
Information and Photographic service. 














Do not miss a single issue of 


Astronomy Now 


Britain's leading astronomical magazine 


Edited by well known astronomer and 
regular contributor to Practical Electronics 
Dr. Patrick Moore CBE 
Place a regular order with your newsagent or for £15-00 
(overseas £18-00) take out an annual subscription from Intra Press, 
Intra House, 193 Uxbridge Road, London W12 9RA 


UTORKIT icroktectronics Tutors 


anual 





















; Siices trom Including instructionm 
Logic Tutors and patch leads ug 


OP Amp Tutors ‘ai 
|.C. Patchboards £2750 | 
GCSE Units PLUS VAT 
Computer Interfaces 
















— *used by hundreds of schools 
», in U.K. and overseas. 



















TUTORKIT PRODUCTS i. : 3 
(Div of Limrose Electronics Ltd) . a 2 
Liay Industrial Estate 
Wrexham, Clwyd, U.K. 
LL12 OTU. Tel 097 883 2285 







Overseas distributors wanted 





PRACTICAL ELECTRONICS AUGUST 1989 47 











r) 
No. 1 LIST BAKERS DOZEN PACKS 
All packs are £1 each, if you order 12 then you are entitled 
to another free. Please state which one you want. Note 
the figure on the extreme left of the pack ref number and 
the next figure is the quantity of items in the pack, finally 
a short description. 

BD2 5 13A spurs provide a fused outlet to a ring main where 

_ devices such as a clock must not be switched off. 

BD7 4 _ Inflex switches with neon on/off lights, saves leaving things 
switched on. 

BD9 2 6V 1A mains transformers upright mounting with fixing 
clamps. 

BD11 1 6%in speaker cabinet ideal for extensions, takes our 
speaker. Ref BD137. 

BD13 12 30 watt reed switches, it's surprising what you can make 
with these — burglar alarms, secret switches, relay, etc., etc. 

BD22 2 25 watt loud speaker two unit cross-overs. . 

BD29 1 B.O.A.C. stereo unit is wonderful breakdown value. 

BD30 2 __Nicad constant current chargers adapt to charge almost any 
nicad battery. 

BD32 2 Humidity switches, as the air becomes damper the 
membrane stretches and operates a microswitch. 

BD42 513A rocker switch three tags so on/off, or change over with 
centre off. 

BD45 1 24hr time switch, ex-Electricity Board, automatically adjust 
for lengthening and shortening day original cost £40 each. 

BD49 10 Neon valves, with series resistor, these make good night 
lights. 

BD56 1 Mini uniselector, one use is for an electric jigsaw puzzle, we 
give circuit diagram for this. One pulse into motor, moves 
switch through one pole. 

BD59 2 Flat solenoids — you could make your multi-tester read AC 
amps with this. 

BD67 1 Suck or blow operated pressure switch, or it can be 
operated by any low pressure variation such as water level 
in water tanks. ; 

BD91 1 Mains operated motors with gearbox. Final speed 16 rpm, 2 
watt rated. 

BD103A 1  6V750mA power supply, nicely cased with mains input and 
6V output leads. 

BD120 2 Stripper boards, each contains a 400V 2A bridge rectifier 
and 14 other diodes and rectifiers as well as dozens of 
condensers, etc. 

BDi22 10m _ Twins screened flex with white pvc cover. 

BD126 10 Very fine drills for pcb boards etc. Normal cost about 80p 
each. 

BD132 2 Plastic boxes approx 3in cube with square hole through top 
so ideal for interrupted beam switch. 

BD134 10 Motors for model aeroplanes, spin to start so needs no 
switch. 

BD139 6 Microphone inserts — magnetic 400 ohm also act as 
speakers. 

BD148 4 Reed relay kits, you get 16 reed switches and 4 coil sets with 
notes on making c/o relays and other gadgets. 

BD149 6 Safety cover for 13A sockets — prevent those inquisitive little 
fingers getting nasty shocks. 

BD180 6 Neon indicators in panel mounting holders with lens. 

BD193 6 Samp 3 pin flush mounting sockets make a low cost disco 
panel. Need cable clips 

BD196 1 in flex simmerstat — keeps your soldering iron etc. always at 

the ready. 

BD199 1 Mains solenoid, very powerful, has 1in pull or could push if 
modified. 

BD201 8 Keyboard switches — made for computers but have many 
other applications. 

BD210 4 Transistors type 2N3055, probably the most useful power 
transistor. 

BD211 1 Electric clock, mains operated, put this in a box and you 
need never be late. 

BD221 5 12V alarms, make a noise about as loud as a car horn. 
Slightly soiled but OK. 

BD242 2  6in x4in speakers, 4 ohm made from Radiomobile so very 
good quality. 

BD252 1 Panostat, controls output of boiling ring from simmer to boil. 

BD259 50 Leads with push-onb '4in tags — a must for hook-ups — 
mains connections etc. 

BD263 2 Oblong push switches for bell or chimes, these can mains 
up to 5 amps so could be foot switch if fitted into pattress. 

BD268 1 Mini 1 watt amp for record player. Will also change speed of 
record player motor. 

BD275 1 Guitar mic - clip-on type suits most amps. 

BD283 3 Mild steel boxes approx 3in x 3in x 1in deep — standard 
electrical. 

BD293. 50 Mixed silicon diodes. 

BD296 2 Car plugs fit into lighter socket. 

BD305 1 Tubular dynamic mic with optional table rest. 

BD400 4 Books, useful for beginners, describes amplifiers, 
equipment and kit sets. 

BD653 2 Miniature driver transformers. Ref. LT44. 
20k to 1k centre tapped. 

BD553a 2  3.5V relays each with 2 pairs changeover contacts. 


Most other packs still available and you can choose any as your free one. 
CAMERAS, Three cameras, all by famous makers, Kodak, etc. One disc, one 
35mm and one instamatic. All in first class condition, believed to be in perfect 
working order, but sold as untested. You can have the three for £10 including 
VAT, which must be a bargain — if only for the lenses, flash gear, etc. Our ref 
10P58. 

675 VOLT MAINS TRANSFORMER PCB mounting, 20va. A very well made 
(British) transformer. Ideal for |aser power supply, etc. Price £4. Our ref 4P38. 
PRETTY CASSETTE PLAYER In handy carrying pouch with silk type 
shoulder cord. Ideal present for young girl. New, tested and in perfect order. 
Just needs headphones and batteries. Price £4. Our ref 4P35. 

EXTRA SPECIAL CROC CLIPS Medium size, just right for most hook-ups. 
Normally sell for around 10p to 15p each. These are insulated and have a 
length of wire connected to them but this is very easy to snip off if you do not 
need it. 20 for £1. Our ref BD117A. 

IONISER FOR YOUR CAR Experts say that positive ions predominate in acar 
and can cause you to feel sleepy so we now offer a car ioniser to counteract 
this. It plugs into the cigarette lighter socket. Price £12 for the complete kit. Our 
ref 12P8. Our famous transformer operated room ioniser is still available at 
£12.50. We claim this to have ten times ore output of ions than the ETI, the 
Equaliser and in fact most other popular kits and ready built ionisers. 
COPPER CLAD PANEL for making PCB. Size approx 12in long x 814in wide. 
Double-sided on fibreglass middle which is quite thick (about'Asin) so this 
would support quite heavy components and could even form a chassis to hold 


a mains transformer, etc. Price £1 each. Our ref BD683. 
5 








POWERFUL IONISER 
Generates approx 10 times more IONS than the ETI and similar 
circuits. Will refresh your home, office, workroom, etc. Makes you 
feel better and work harder — a complete mains operated kit, case 
included. £12.50 plus £2 postage. Our ref 12P5/1. 





48 












MODERN TELEPHONES Two- 
piece push-button desk or wall 
mounting telephone. Fitted with 
standard BT flat plug for immediate 
use. Standard model £8. Our ref 
8P31. Or similar but with 10 
memory feature £10. Our ref 
10P68. If not collecting add £2 for 
special packing. 

ORGAN MASTER Is there a three octave 
musical keyboard. It is beautifully made, has 
full size (piano size) keys, has gold plated 
contacts and is complete with ribbon cable 
and edge connector. Can be used with many _ 
computers. We can supply information Q 
sheet. Brand new, only £15 plus £3 postage. 
Our ref 15P15. 


ELECTRONIC SPACESHIP Sound and impact controlled, responds to claps 
and shouts and reverses when it hits anything. Kit with really detailed 
instructions. Ideal present for budding young electrician. A youngster should 
be able to assemble but you may have to help with the soldering of the 
components on the pcb. Complete kit £8. Our ref 8P30. 


DATA RECORDER FOR COMPUTERS For playing games or listening to 
music cassettes. It has a built-in condenser microphone and loud speaker 
(muted if you use the extension socket. Has the following controls: pause, 
Stop/eject, fast forward, rewind, play and record. Also have built-in tape 
counter, extension headphone and microphone socket and volume control. 
Built-in power supply enables it to run from the mains but provision also for 
battery operation. In ‘as new’ order condition, but customer returns so may 
have fault. Price only £10 and if you order 4 you get a fifth one free. Our ref 
10P65. 


BUSH RADIO MIDI SPEAKERS Stereo pair, BASS reflex system, using a full 
range 4in driver of 4ohms impedance. Mounted in very nicely made black 
fronted walnut finish cabinets. Cabinet size approx 8'in wide, 14in high and 
3'Zin deep. Fitted with a good length of speaker flex and terminating with a 
normal audio plug. Price £5 the pair plus £1 post. Our ref 5P141. 


312 FLOPPY DISC DRIVE - DOUBLE SIDED, DOUBLE DENSITY, 80 
TRACK Shugart compatible, has 34 way IDC connect and will interface with 
almost any computer. Made by the famous Japanese NEC Company. Price 
£59.50 plus £3 insured post. 





DIALING BUTTONS 


REDIAL BUTTON 


ATARI 65XE 
COMPUTER 


i At 64k this is most powerful and 
suitable. for home and business. 
Brand new, complete with PSU, TV 
lead, owner's manual and six 
games. Can be yours for only £45 
plus £3 insured delivery. 


65XE COMPENDIUM Contains: 65XE Computer, its data recorder XC12 and 
its joystick, with ten games for £62.50 plus £4 insured deliver. 

AGAIN AVAILABLE: ASTEC PSU Mains operated switch mode, so very 
compact. Outputs: + 12v 2.5A, +5v 6A, + 5v 5A, + 12v .5A. Size: 7% long x 
4%in wide x 2%in high. Cased ready for use. Brand new. Normal price £30+, 
our price only £10. Our ref 10P34. 

VERY POWERFUL 12 VOLT MOTORS. ‘4rd Horsepower. Made to drive the 
Sinclair C5 electric car but adaptable to power a go-kart, a mower, a rail car, 
model railway, etc. Brand new. Price £15 plus £2 postage. Our ref 15P8. 


PHILIPS LASER 
This is helium-neon and has a power rating of 2mW. Completely safe as 
long as you do not look directly into the beam when eye damage could 


result. Brand new, full spec. £30 plus £3 insured delivery. Mains 
operated power supply for this tube gives 1kv striking and 1.25kv at 5mA 
running. Complete kit with case £15. Battery operated P.S.U. now 
available at £16. 





BATTERY DRIVEN LASER POWER SUPPLY This is available in three 
versions: Firstis a cased unit which holds the power supply and is fed from a 
separate 12volt battery and drives the laser through extension leads. Kit 
complete with ABS case. Price £15, Our ref 15P22. Secondis a metal cased 
unit which holds the power supply and the laser but is driven from an external 
12volt battery. This unit, in kit form, costs £18. Our ref 18P2. A conversion kit 
from 15P22 to 18P2 is £6. Our ref 6P14. Third is a metal cased unit which 
holds the laser, its power supply and 2 x 6volt rechargeable batteries which 
feed it, also the mains driven unit to recharge the batteries. Complete kitif £24. 
Our ref 24P2. 


HAND-HELD VIDEO LAMP. Main operated and will enable you to take 
professional standard videos. Made by the famous Ferguson Company, this 
uses a 1000w halogen lamp in a fan cooled, hand-held and hand switched 
metal housing. Comes complete with option of barn-door assembly and 
camera bar. Obviously intended to retail at over £60, we offer these as £30 
each plus £3 insured delivery. Our ref 30P3. 

HIGH RESOLUTION MONITOR. In black and white, used Philips tube M24/ 
305W. Made up in a lacquered frame and has open sides. Made for use with 
OPD computer but suitable for most others. 5 and new. £16 plus £5 post. Our 
ref 16P1. 


12 VOLT BRUSHLESS FAN. Japanese made. The popular square shape 
14% x 4% x 17in). The electronically run fuse not only consume very little 
current but also they do not cause interference as the brush type motors do. 
Ideal for cooling computers, etc. or for a caravan. £8 each. Our ref 8P28. 


MONO RADIO CASSETTE RECORDER AM/FM with all the normal controls. 
In ‘as new’ condition but customer returns or shop rejects, so may need 
attention. Price £10. Order 5 of these and get a sixth one free. Our ref 10P66. 







FDD BARGAIN 
3%in made by Chinon of Japan. Single aided, 80 track, Shugart 
compatible interface, interchangeable with most other 3% in end 5%in 
drives. Completely cased with 4 pin power lead and 34 pin computer 
lead £40. Plus £3 ins del. Our ref 40P1. 


MINI MONO AMP on p.c.b. size 4” x 2” (app.) 
Fitted volume control and a hole for a tone con- 
trol should you require it. The amplifier 
has three transistors and we estimate 
the output to be 3W rms. More 
technical data will be included 

with the amp. Brand new, perfect 
condition, offered at the very low 

price of £1.15 each, or 13 for £12.00. 


J & N BULL ELECTRICAL 
Dept PE, 250 PORTLAND ROAD, HOVE 
_ BRIGHTON, SUSSEX BN3 5QT 
MAIL ORDER TERMS: Cash, PO or cheque with order. Orders under 
£20 add £1.50 service charge. Monthly account orders accepted from 


schools and public companies. Access and B/card orders accepted 
minimum £5. Phone (0273) 734648 or 203500. 


















POPULAR ITEMS 


Some of the many items described in our current list "ar 
which will you receive if you request it 


BATTERY OPERATED TRAVEL MECHANISM On a plastic panel 
measuring approx Yin x 3%Ain. Is driven by a reversible 12v battery motor, 
fitted with pulley and belt which rotates a threaded rod and causes a platform 
to travel backwards and forwards through a distance of approx 5in. Price £5. 
Our ref 5P140. 


MAINS OPERATED WATER VALVE with hose connection for inlet and 
outlet suitable for low pressure. Auto plant watering, etc. Only £1 each. Our ref 
BD370. 


20 VOLT 4 AMP MAINS TRANSFORMER Upright mounting with fixing feet. 
Price £3. Our ref 3P59. 


12 VOLT SOLENOID Has good ‘4in pull or could be made to push if fitted with 
a rod. Approx 1'in long by 1in square. Price £1. Our ref BD232A. 


160HM PM SPEAKERS Approx 7in x 4in. 5 watts. Offered at a very low price 
SO you can use two in parallel to give you 10 watts at 8 ohms. £1 for the two. 
Our ref BD684. 


EHT TRANSFORMER 4kv 2mA Ex-unused equipment. £5. Our ref 5P139. 


FOIL CAPACITORS Axial ended .33uf 1,000v. 4 for £1. Our ref DB672, Many 
other sizes in stock, send for May newsletter. 


4 CORE TINSEL COPPER LEAD As fitted to telephones, terminating with flat 
BT plug. 2 for £1. Our ref BD639. 


EHT TRANSFORMER 8kv 3mA. £10. Our ref 10P56. 


DOUBLE MICRODRIVES We are pleased to adivse you that the Double 
Microdrives which we were offering at about this time last year as being for the 
‘QL’, ‘OPD' and several other computers are again available, same price as 
before namely £5. Our ref 5P113. 


VERY USEFUL MAGNETS Fiat, about 1in long, ‘in wide and ‘in thick. Very 
powerful. 6 for £1. Our ref BD274(a). 


ACORN COMPUTER DATA RECORDER REF ALF03 Made for the Electron 
or BBC computers but suitable for most others. Complete with mains adaptor, 
leads and handbook. £10.00. £2 special packing. Ref 10P44. 


FREE POWER! Can be yours if you use our solar cells — sturdily made 
modules with new system bubble magnifiers to concentrate the light and so 
eliminate the need for actual sunshine — they work just as well in bright light. 
Voltage input is .45-you join in series to get desired voltage — and in parallel 
for more amps. Module C gives 400mA, Price £2, Our ref. 2P199 Module D 
gives 700mA, Price £3, Our ref. 3P42. 


SOLAR POWERED NI-CAD CHARGER 4 Ni-Cad batteries AA (HP7) 
charged in eight hours or two in only 4 hours. It is a complete, boxed ready to 
use unit. Price £6. Our ref. 6P3. 


METAL PROJECT BOX Ideal size for battery charger, power supply etc,; 
sprayed grey, size 8in x 4/in high, ends are louvred for ventilation other sides 
are flat and undrilled. Order Ref. 2P191. Price £1. 


4-CORE FLEX CABLE. Cores separately insulated and grey PVC covered 
overall. Each copper core size 7/0.2mm. Ideal for long telephone runs or 
similar applications even at mains voltage. 20 metres £2. Our ref 2P196 or 100 
metres coil £8. Order ref 8P19. 


6-CORE FLEX CABLE. Description same as the 4-core above. Price 15 
metres for £2. Our ref. 2P197 or 100 metres £9. Order ref. 9P1. 


13A PLUGS Good British make complete with fuse, parcel of 5 for £2. Order 
ref. 2P186. 


13A ADAPTERS Takes 2 134A plus, packet of 3 for £2. Order ref. 2P187. 


28V -0- 20V Mains transformers 2 amp (100 watt) loading, tapped primary. 
200-245 upright mountings £4. Order ref. 4P-24. 


BURGLAR ALARM BELL - 8” gong OK for outside use if protected from rain. 
12V battery operated. Price £8. Ref. 8P2. 


CAPACITOR BARGAIN — axial ended, 4700uF at 25V. Jap made, normally 
50p each, you get 4 for £1. Our ref. 613. 


SINGLE SCREENED FLEX 7.02 copper conductors, pvs insulated then with 
cooper screen, finally outer insulation. In fact quite normal screened flex. 10m 
fo £1. Our ref DB668. 


M.E.S. BULB HOLDERS Circular base batten type fitting. 4 for £1. Our ref 
DB127s. 


SPRING LOADED TEST PRODS - Heavy duty, made by the famous Bulgin 
company, very good quality. Price 4 for £1. Ref. BD597. 


3-CORE FLEX BARGAIN No. 1 - Core size 1.25mm so suitable for long 
extension leads carrying up to 13 amps, or short leads up to 10 amps. 15mm 
for £2. Ref. 2P190. 


3-CORE FLEX BARGAIN No. 2 - Core size 1.25mm so suitable for long 
extension leads carrying up to 13 amps, or short leads up to 25A. 10m for £2. 
Ref. 2P190. 


ALPHA-NUMERIC KEYBOARD - This keyboard has 73 keys giving trouble 
free life and no contact bounce. The keys are arranged in two number pad, 
board size is approx. 13” x 4” — brand new but offered at only a fraction of its 
cost, namely £3 plus £1 post. Ref. 3P27. 


YeTH HORSEPOWER 12 VOLT MOTOR Made by Smiths, the body length of 
this is approximately 3in, the diameter 3in and the spindle eth of an inch 
diameter. It has a centre flange for fixing or can be fixed from the end by means 
of 2 nuts. A very powerful little motor which revs at 3,000 rpm. We have a large 
quantity of them so if you have any projects in mind then you could rely on 
supplies for at least two years. Price £6. Our ref 6P1, discount for quantities of 
10 or more. 


3 VOLT MOTOR Very low current so should be very stuiable for working with 
solar cells. £1 each. Our ref BD681. 


MINI SPEAKERS to use instead of headphones with your personal steros — 
simply plug in to earphone socket. Excellent sound quality, only £4 per per. 
Our ref 4P34. 


INNER EAR STEREO HEADPHONES Ideal for lady listeners as they will not 
mess up your hair do! Come complete in a neat carrying case. Price £3. Our 
ref 3P56. 


STEREO HEADPHONE AMPLIFIER Very sensitive. A magnetic cartridge or 
tape head will drive it. Has volume control and socket for stereo headphones. 
3v battery operated. £1 each. Our ref BD680. 


FET CAPACITOR MICROPHONE EAGLE C1.200 Output equivalent to a 
high class dynamic microphone while retaining the characteristics of a 
capacitor microphone. Price £1. Our ref BD646. 


SUM-MIN TOGGLE SWITCH Body size 8mm x 4mm x 7mm SBDT with 
chrome dolly fixing nuts. 4 for £1. Our ref BD649. 


SUB-MIN PUSH SWITCH DPDT. Single hole fixing by hexagonal nut. 3 for 
£1. Our ref BD650. 


PRACTICAL ELECTRONICS AUGUST 1989 
















sk anybody, "Quick, off the top of 
y.¥-«: head, what does a robot voice 
sound like?" 

Chances are that the first answer to come 
to mind will be, "A Dalek". Perhaps, after a 
little more thought, fans of Star Wars rather 
than Dr Who will offer, "R2D2", or maybe 
"C3PO". The voice of Hal, the deranged 
computer in 200], might also be another 
response. 


RVieler i s\elelns 


Though I too become enthralled by Star 
Wars, and 2001, on each viewing, my mind 
certainly thinks of the infamous and exter- 
minatory Daleks as the root for all mech- 
anical voices. There's something about the 
vibratory clipped accents of the Daleks 
which, for me, makes their voices synon- 
ymous with robots. 

Poor old R2D2, though capable of com- 
municating with other computerised devices, 
could not communicate directly with 
Humanity. And the technology that created 
the voices of Hal and C3PO produced 





Just what the 
Doctor ordered - 
the speedy route 

to chatting In 

robo-speak 





basically created by three processes. First, an 
actor speaks the words into a microphone 
and the signal is duly amplified. It is then 
passed through a ring modulator to produce 
a metallic sound, and finally subjected to 
amplitude variation to give it its vibratory 
effect. 

Ring modulators are really fascinating 
units to work and play with. The theory was 


EASI-BUILD PROJECT 





Rather, the process both adds and subtracts 
the two frequencies to and from each other, 
producing an output signal containing upper 
and lower harmonics of the originals. The 
technique, though, is beyond the scope this 
simple project, which is based upon just the 
vibratory effect associated with the Dalek- 
type voice. | 


CLIPPED ACCENTS 


In Fig.1 you will see that the circuit 
consists of four opamps, contained in one 
package, and a transistor. The purpose of 
IC1a is to control the gain of the input voice 
signal. Most ordinary high output crystal 
microphones will produce a signal strong 
enough to suit the circuit. Lower output level 
microphones will need to have their signal 
preamplified first before being sent through 
the unit. The output signal from most cass- 
ette recorders is likely to be sufficiently 
strong to suit the unit without additional 
preamplification. 

The input signal strength can be given a 
small amount of gain by VR1. As I am sure 








VODALEK 








speech as perfect as that from any human, 
so in terms of novelty effects units for 1989, 
their voices are really non-starters. 

Some years ago I rang the BBC and had 
a chat with one of the engineers involved in 
the Dr Who sound effects creation. He told 
me that the true Dalek voice, as produced 
by the BBC's Radiophonics Workshop, is 





1N4148 


02 
C2 


TR 
2N3819 


R14 100k 


PRACTICAL ELECTRONICS AUGUST 1989 


BY JOHN BECKER 


examined in my constructional project 
published in PE Nov-Dec 84. In essence, an 
input signal is mixed with a secondary 
signal of a variable frequency, but not in the 
manner associated with ordinary mixers. 





R7 510k 


OUTPUT 


IC1=LM324 
PIN & =+VE 
PIN 11= GND (OV) 


Fig.1. Complete circuit 
diagram for the Vodalek 


many readers will be aware, the gain is rela- 
ted to the value of VR1 plus R3, divided by 
the value of R2, plus 1. In this case the maxi- 
mum gain is ((10k + 500k) / 10k) + 1 = 52. 

However, I have included two diodes, D1 
and D2 in the feedback path across [Cla. 
These have the effect of restricting the 
maximum output level to about 0.6V peak 
to peak. In other words they clip the signal, 
giving it a squarish shape if viewed on an 
oscilloscope. The effect is a harsher sound 
than would otherwise be experienced, and 
one which is more consistent in level. C2 is 
used to filter out some of the upper frequen- 
cies of the voice signal, so also changing its 
quality. 


HIGHER 


EXTERMINATION 





The signal is then fed through the section 
associated with the modulation process to 
the filter circuit around IC1b. This also 
modifies the frequency characteristics and 
the resulting sound quality. Although all of 
the components associated with IC1b play 
their part in the filtering process, C4 and C5 
are the principle controllers. Increasing their 
value will decrease the frequency range, 
and viceversa, but it is preferable, though 
not essential, to keep their values within the 
same ratio. 

From IC1b the modified signal is simply 
taken via C6 to the output level control 
VR3. From there it can be fed to any 
normal amplifier. 


49 








COMPONENTS 


RESISTORS 


Ri, R2,.R3 10k (3 off) 
R4-R6, R13, R14 100k (5 off) 


220n polyester 

470p polystyrene (2 off) 
15n polyester (2 off) 

In polystyrene 

1pF 63V electrolytic 
22uUF 16V elect (4 off) 
100n polyester 


POTENTIOMETERS 


500k lin mono rotary 
100k skeleton preset 
10k log mono rotary 
10k lin mono rotary 
1M lin mono rotary 


SEMICONDUCTORS 


1N4148 
2N3819 fet 
324 quad opamp 


MISCELLANEOUS 


PP3 battery clip, pcb supports (4 off), 
knobs (4 off), 14-pin ic socket,mono jack 
sockets (2 off), spst switch, Phonosonics' 
PCB type number 155A,box to suit, 
connecting wire and solder. 


WOBBULATING | 


The modulating oscillator consists of the 
circuit around IClc and ICld. You've no 
doubt seen many circuits with oscillators 
that look similar to this one. If you haven't 
you can add it to your list of possible 
candidates for frequency generator sources. 
I gave two other types in the Wheeby-Jeeby 
project of PE June 89. The circuit oscillates 
at a rate set by the value of C8 and the 
feedback resistance across R14 and the rate 
controller VR5. I showed and described a 
similar circuit in the Oscilloscope articles of 
PE Nov 88 to Jan 89. The circuit oscillates 
because each time the output of ICIc rises 
above or drops below the reference level at 
the comparator IC1d, the comparator changes 
Output state, so reversing the direction of 
charge for C8. You will see a more sophis- 
ticated variation on this theme in the forth- 
coming Combined Frequency Counter and 
Twin Signal Generator (scheduled for the 
Sept 89 issue). 

The output at ICld is a squarewave, which 
in this instance we don't need. What we are 
interested in is the triangular waveform 
produced at the output of IClc. It is taken 
via C11, through the level control VR4, and 
to the amplitude controller around TR1. 








50 


BATTERY +VE 


BATTERY 
- VE (OV) 


(SV TO 15V) 


VR1 VR 
INPUT GAIN SPEED 


Fig. 2. (top) Printed circuit 
board layout. 

Fig.3. (above) Suggested box 
and controls layout. 





TRI is a field effect transistor (fet) whose 
resistance between source and drain is con- 
trollable by the voltage or current present at 
its gate input. Here the basic resistance is 
preset by the voltage supplied via VR2. As 
the current via C10 increases and decreases 
in sympathy with the triangle wave from 
ICic, so the resistance across TR1 also 
changes. Since the signal between IC1a and 
IC1b passes through R4 on its way to IC1b, 
the changing resistance across TR1 causes 
the signal level at the junction of R4 and 
TRI1 to vary up and down. And this of course, 
is just the amplitude modulation that we 
need for a robot type voice. 

A modulation of about 30Hz is the rate I 
find most suitable for creating the robot 
effect, but there is wide range to either side 
of this controllable by VRS. 

The circuit will run from any dc voltage 
between SV and 15V. A 9V battery is ideal. 


[0161562] 1562 


SETTING THE ACT 


Setting-up is very straightforward once 
you've assembled and checked the pcb ass- 
embly. Apply a suitable signal to the input 
and adjust VR2 until the signal is heard to 
modulate smoothly when plugged into an 
amplifier. You will soon find which settings 
for the panel control pots are best suited to 
different effects needs. 

Final points - VR1 at too high a setting 
will also allow any noise near the micro- 
phone to be amplified and cause it to be 
modulated as well as the speech. Also note 
that if the unit is plugged into an amplifier 
having a good bass response it may be 
necessary to reduce the bass control on the 
amp to cut out the sound of the modulator, 
which might otherwise be heard in quiet 
passages. For the best overall robot-type 
effect, you should speak in a monotone, 
slowly, and with long drawn out words. 

So, have fun with this Vodalek. Play the 
part, utter your words of dooming extermi- 
nation, and even Time-Lords might tremble! 


PRACTICAL ELECTRONICS AUGUST 1989 





















Wy + LEARN BY BUILDING « ENJOY BY USING «x ASTRONOMY 


“<%= PROJECT KITS 


DESIGN 

FEATURES 

* BE CREATIVE x RAISE YOUR SKILLS x GET KITTED! « 
COMPUTER KITS 


The software listings published with the computer kit 
projects are for use with C64, PET and BBC computers. 
CHIP TESTER SET258F £41.50 
Computer controlled logic and chip analyser. 

EPROM PROGRAMMER SET277 £26.20 
Computer controlled unit for 4K Eproms. 
MICRO-CHAT SET276 £69.50 
Computer controlled speech synthesiser. 
MICRO-SCOPE SET247 £49.50 
Turns a computer into an oscilloscope. 
MICRO-TUNER SET257 £57.40 
Computer controlled, tuning aid and freq counter. 
MORSE DECODER SET269 £26.70 


Computer controlled morse code-decoder. 























SIDEREAL CLOCK 
SET295 £49.50 
Dual purpose star-time and 
solar-time digital clock with 
alarm. 






























ENVIRONMENT 
WEATHER CENTRE 


Keep the Met Office in check and monitor the wind speed 

and direction, rain, temperature, soil moisture and sunny 

days. 

Six detector circuits — KIT 275.1 £18.50 

Automatic metered control monitor circuit — KIT 275.2 
£41.50 

Optional computer control circuit — KIT 275.3 £15.50 


ELECTRONIC BAROMETER 
SET285 £41.20 


Computer controlled unit for monitoring atmospheric 
pressure. 


GEIGER COUNTER SET264 £65.50 
A nuclear radiation detector for environmental and 
geological monitoring. With built in speaker, meter and 
digital output. This project was demonstrated on BBC TV. 


ORDERING 


Add 15% VAT. Add P&P — Sets over £50 add £3.00. 
Others add £2.00. Overseas P&P in catalogue. Text 
photocopies — Oscilloscope £3.00, Geiger £3.00, 
Weather £2.00, others £1.00, plus 50p post or large 
SAE. Insurance 50p per £50. MAIL ORDER, CWO, CHQ, 
PO, ACCESS VISA. Telephone orders: Mon-Fri, 9am — 


















DUAL BEAM OSCILLOSCOPE 

2Y-amps, 6 ranges, variable level, DC to over 1MHz. 4 
modes — Y1, Y2, Y1 & Y2, Y1 & Y2 to X. Time base 
variable from 0.05Hz to 20KHz. Variable sync level, 
polarity and source. Separate bright-line, brilliance and 
focus controls. Independent trace deflection controls. 
Details in catalogue. 





BURGLAR ALARM 
CONTROLLERS 


MULTIZONE CONTROL 
SET280 £23.90 


Two entry-zones, anti-tamper loop, personal attack, entry- 
exit timing, timed duration, automatic resetting, latching 
LED monitors. 


SINGLE ZONE CONTROL 
SET279 £10.50 


With timed duration control and latching LED monitor. 
Both units can be used with any standard detection 


devices, such as contact or magnetic switches, pressure 6pm. 0689 37821. (Usually answering machine). 
pads, tremblers, ultrasonics, infrared etc., and will 


activate standard bells, strobes or sirens. MORE KITS IN CATALOGUE 


PHONOSONICS, DEPT PE98, 8 FINUCANE DRIVE, ORPINGTON, KENT, BR5 4ED. MAIL ORDER 


CRICTALEWOOD 
now: VELECTRONICS cS 


e rN 
J Q S 100 PAGE COMPONENT =£>SC-\\S <\y> 
CATALOGUE PRICES! 


SEND OFF FOR YOUR COPY TODAY 





PE EASI-BUILD SERIES 
PLUS 


PE HAND CLAPPER 
SEE CATALOGUE 


VARIOUS 
VOICE SCRAMBLER SET287 —_ £49.50 


32 switchable channels to keep your communications 
confidential. 

STORMS! £35.50 each unit 
Raw nature under panel control! Wind & Rain SET250W. 
Thunder & Lightning SET250T. 

DISCO-LIGHTS SET245F £69.50 


3 chan sound to At chasers, auto level. 


EVENT COUNTER SET278 £36.60 


















































4-digit display counting for any logic source. 












FREE VOUCHERS! 


SEND OFF FOR YOUR CATALOGUE 





AND VOUCHERS TODAY. 
I WOULD LIKE TO RECEIVE... Tape your $1 coin 
COPY(COPIES) OF THE 1989 here, or senda 


iO 7 CRICKLEWOOD ELECTRONICS cheque or postal 
Lv COMPONENT CATALOGUE. I order for £1.00 for 
ATS 7 t ay , < ENCLOSE 6...... every catalogue you 
ELSIN BOR RES ss 4 ot a ‘2 PLEASE ENCLOSE MY FREE require. 
2: VOUCHERS. RE 


rrrrrrrrerrr rr rererr reer errr rrr ere 


POUUUEUUPUTICTOOE OE 


CLO n Ae ie af VERS OO 8 SO Sin POS th eh tole clic dees cco ea RIES, | MMC a aia a ae 


PPUUERETETTTETUTET TT, 


PRACTICAL ELECTRONICS AUGUST 1989 51 











Free 
Reader 


Adverts 


Searching for that elusive 
component? 

Surplus equipment to sell? 
Read the rules and fill in 
the form below to have 
your free ad published in 
PE BAZAAR. 













Wanted: 41256 drams 16. Please 
must be cheap. Mondays or 
evenings only. Hastings 424382. 


Wanted: service manual for 
Thandar SC110 oscilloscope. 
Photocopy accepted. Telephone 
A/H (+31) 239716. Mr. S. Beukes, 
#2, 340 Florida Road, Durban 
4001, South Africa. 

All my surplus components for 
sale. Good assortment £3 or send 
sae for lists. J. Allen, 150 
Magheralane Road, Antrim, Co. 
Antrim BT41 2PD. 

Constructor 59-80 R+EW 81-83 
E.E. 78-83 P.E. 78-89. Wanted 
manual for Cossor 1049 MK4 
scope. J.Rudrum, 2 Princes Road, 
Eastbourne, E. Sussex BN23 6HG. 


Seven surplus Tektronix 
oscilloscope modules LA545-54- 
CA, LAS545-54D and_— two 


northeastern frequency converters 
model 14-21C. Offers please. Mr. 
A. Ireson, 30 Avenue Road, 
Wellingborough, Northants NN8 
4EP. 

Wanted: E.H.T. unit or transformer 
for telequipment D.M. 64 'scope in 
working condition. Phone (0254) 
662423. 


- 
| PE BAZAAR 





Name & Address 


AR88LF 6555s, 741s BC108s, 
LEDs, 8 pin + 14 pin sockets, 
connecting wire £5.25 per bag. No 
dealers. By post. Mr. D. Martin, 6 
Downland Garden, Epsom, Surrey 
KT18 5SU. 

Eprom Programmer/PLC/Panel. 
Brand new. Worth £500. Accept 
£175 ono. Tel: (0789) 295883 
daytimes. 

4-Data teletext adaptor for ZX 
Spectrum - view, store and print 
Ceefax and Oracle pages; download 
telesoftware. £79 with manual and 
transformer. Mr. W. Kurek, 150 
Sandon Road, Stafford, Staffs ST16 
3HG. 

Rotary position encoder £20. 
Baudot code printer £20. Mr. G. 
Fisher, 9 Aspen Drive, 


_ Countesthorpe, Leics LE8 3SA. 


I am interested in Satellite 
television. I have complete 
equipment and I am looking for 
partners. Ing Jan _ Luteran, 
Prostejovska 7, 08001 Presov, 
Czechoslovakia. 

Superb quality monitor, Cotron 
PDM17, completely flat 6 inch 
tube, never used, offers around 
£600. Tel: Martin (0344) 427983. 
Practical Electronics April 1976 
to December 1980. Offers plus 
p&p. A.J. Chadwick, 36 Ella Street, 
Hull HU5 3AY. Tel: (0482) 445824. 
PE Gemini amplifier stereo 30 
watts £20. Goldring turntable £10, 
Sharp stereo cassette deck hardly 
used £30. P.J. Worden, 17 Brocket 
Close, Chigwell, Essex IG7 4ET. 
Ferguson Video camera, recorder, 
tuner, spare battery. Cost £1400, 
accept £290. (0625) 24822 
Macclesfield. 

Drams: 4116 ex. eqpt. £1 each. 
8251 USART £2. Z80A CPU £1 
CTC £1.50. Full list available. 41 
Aldworth Close, Bracknell, 
Berkshire. RG12 4AW. Tel: (0344) 
51433. 

Philips V2000 VCR 14-day timer, 
8 hours per tape etc. for repair or 
parts £10. Mr. Clemow Tel: (0895) 
53890. 


setatatetatetetatetatetetetetateteteteetetatetetetetetetatetesetrcseccetseesesecscenenesesecececereratetetetereratatatetetetaatetetetetatatetetetetstetetetetetetetetete 


slellelelnielelceleteeleteleteleletaseleletetateletaseleteleteteletelelateleleteteleteleteteleteteleteleteteleteteleteteteteleteteleteteleteteleteteteteteteteletetetetetetetetetetetetetetetetetetets 


Wanted: point contact and other 
early types of transistor. Write for 
lists and prices. Andrew Wylie, 2E 
Welbeck Mansions, Inglewood 
Road, London NW6 1QX. 

Wanted: wide carriage printer for 
Atari ST 9 or 24 pm. Tel: (0909) 
566695. 

Cossor CDU 150/CT531/3 dual 
trace oscilloscope with handbook. 
Cost £242 SH but not used. Accept 
£100 ono. R. Harding, 10 Sands 
Farm Drive, Burnham, Slough SLI] 
7LD. Tel: (0628) 603048. 

Swap Olympus OM10 _ SLR 
camera for WS2000 modem or 
similar W.H.Y. D. Rowlands, 7 Bro 
Silyn, Talysarn, Caernarfon, 
Gwynedd, North Wales LL54 6AU. 
Wanted: meter movement for AVO 
valve. Characteristic meter. Grey 
case hinged lid sloping front black 
handles. P.J. Gallagher, 42 New 
Street, Macroom, Co. Cork, Ireland. 
Tel: 026 41131. 

CBM 64 with JCL IEEE 488 
interface. How does one load "Easy 
Script". Please tel: (0232) 642687 
after 6pm. Mr. C. Salter, 19 
Saintfield Road, Belfast BT8 4AF. 
Apple IIE duodisk 128K green 
monitor 80COL Z80 card joystick 
dot matrix printer. Bargain £4.50 
ono. S. Chowdhary, 62 Knightwood 
Crescent, New Malden, Surrey. Tel: 
01-336 2307. 

For Sale: video enhancer (Ken- 
multi). List price £39.95. Wanted 
£22.50. Tel: (Bath) 874138. Ask for 
Richard. 

Tektronix 453 dual trace 50 MHz 
delay sweep oscilloscope in lst 
class working order £250. Phone: 
(0293) 513787 eve. 

Solartron dual beam oscilloscope, 
(valve type). Manual and/or circuit 
diagram, also test leads, wanted. 
State price. J.W. Dixon, 19 Salkeld 
Road, Penrith, Cumbria CA10 1ND. 
Wanted: RPY58A photoresistor for 
dark activated switch. Edward 
Murray, Old Cardinham, Bodmin, 
Cornwall PL30 4ED. Tel: 020882 
496. 


a SS Me Be EE ee | eT 
Please publish the following small ad. FREE in the 


next available issue. I am not a dealer in electronics or 


associated equipment. I have read the rules. 
Signature...... 






RULES Maximum of 16 words plus address and/or 
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can be placed in our classified columns). Items related to 
electronics only . No computer software. PE cannot accept 
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Send this form (or a photocopy of it) to: 

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ees sine Sus: Sm: Semi tae Shek oa omy ese Tan eer aor al 


PRACTICAL ELECTRONICS AUGUST 1989 














PE COMPETITION RESULTS 


a 
PE COMPETITION RESULTS _ 
FORUM QUORUM! 





IT'S TIME TO TELL 
WHO'S RUNG THE BELL 
IN OUR TELEPOINT 
TELEPHONE COMPETITION 


AND HERE'S THE LINE UP OF THE FIVE 
FORTUNATE WINNERS WHO HAVE EACH 
WON A FORUM TELEPOINT PERSONAL 
TELEPHONE : 


Rem Plenzik of Broadstairs, Kent 

S.A. Connolley of Blackpool, Lancs 

Mick Jeffreys of West Melton, Rotherham 
Andrew J. Bateman of London WC1 

S.L. Hurcombe of Kerrys Gate, Hereford 


Congratulations and happy hi-tech 
telecomms to all of you! 


THE ANSWERS 


With questions one to three these are the answers for 
which I was looking : 

The first communications satellite was launched in 
1962 and was called Telstar. Alexander Bell is credited 
with inventing the telephone. 

Most entrants had these three answers correct, 
though a fair number believed that 1955 was the 
launch date. A few suggested that 1969 and 1975 were 
the correct years. Almost unanimously Telstar was 
given as the answer to question two and only a very 
small minority believed that Astra and Buzbysat were 
the satellite names. Buzbysat is (so far as I know) a 
fictitious name invented by myself. Astra is the satellite 
recently launched for use by Sky Satellite TV. 

Alexander Graham Bell seems to be universally 
acclaimed as the inventor of telephone. Very few of you 
fell into the trap of honouring Hans Fernsprecher or 
Gugliemo Marconi for the invention. Marconi, of 
course, should be honoured for the invention of 
wireless. Fernsprecher is a name I coined to confuse 
you - those who speak German may recognise the pun! 

The answer to question four disturbed many of you. It 








also disturbed me! My source book for the date was a 
somewhat ancient and cheap volume claiming to be an 
encyclopaedia. It quoted 1861 as the year in which Bell 
invented the telephone. A totally fallacious assertion! 
As so many of you pointed out, 1876 is the date 
acknowledged by history. However, a fair number of 
you seem to possess equally fallacious documentation, 
claiming that your books variously gave 1871, 1878, 
1875, and even 1856. 

The truth appears to be that the microphone (albeit, a 
very crude one) was invented in 1861, by a certain 
Johann Philip Reis. Bell first demonstrated the 
telephone at the Philadelphia Exhibition of 1876, and 
this is the same year in which he filed his patent, 
believed to be on March 7th under US patent number 
174465. It's conceivable that he actually invented the 
telephone before 1876, but this is the year I now accept 
as factual. If anyone knows differently, please tell me! 
As far as the draw was concerned, both 1861 and 1876 
were taken as valid answers. 

Questions five to seven were survey queries and your 
answers played no part in the draw. Thank you all for 
your opinions. 

Our thanks too to Shaye Communications for kindly 
making available the Forum Telepoint telephones. 


RASA SA ERA SAAR AEN IMRT NED RT ROD MACRO RIE RENO A AREER DOES SORE NS 


PRACTICAL ELECTRONICS AUGUST 1989 


52 














=p) Eloy: Wale)\’ 


FULL-TIME 
TRAINING 
COURSES 


2 YEAR 
BTEC NATIONAL DIPLOMA 
Electronics and 
Communications 
Engineering 
(TV, Computers,Programming,!T) 


1 YEAR | 
BTEC NATIONAL CERTIFICATE 
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2.Computing Technology 
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3. Information Technology 
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4. Software Engineering 
(Assembler, BASIC, Pascal, CADCAM) 


x Those eligible can apply for E.T. grant supportx 


COURSES COMMENCE 
Monday 18th Sept. 1989 


LONDON ELECTRONICS 
COLLEGE 
Dep: AA, 20 Penywern Road, 


Start training now for 
the following courses. 
QO Telecomms Tech C&G 271 
Q Radio Amateur Licence C&G 
QO) Microprocessor 
Q Introduction to Television 






















Send for our brochure - without obligation or 


telephone us on 06267 79398 (Ref: PE5/89) 


Radio & Telecommunications 
Correspondence School, 
12 Moor View Drive Feignmouth, 
Devon TQ14 9U 





54 













Reach thousands of serious electronic and computer enthusiasts. Advertise in PE Classified 
pages: Rates 20p per word or £8.50 per single column cm (plus VAT). All classified 
advertisements must be pre-paid. Send your copy 
or payment by Visa or Access accepted) to: Practical Electronics, Intra 
Road, London W12 9RA. Tel: 01-743 8888. Fax: 01-743-3062 


LET PE WORK FOR YOU! 





L.F. HANNEY 


77 Lower Bristol Road, Bath, 
Avon. 
Tel: 0225-24811 









Your electronics component specialist for 
AVON, WILTS. & SOMERSET 
Open every day, except on Thursday 


EDINBURGH 


OMNI ELECTRONICS 


stock a wide range of 
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Tel: 031 667 2611 
Open Mon-Fri 9am-6pm 
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Send 2x19 stamps for NEW CATALOGUE! 


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If you are buying Electronics Components 
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For electronics components, leads, 
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books, magazines etc.,etc.,etc., 
Multilode Ltd. 7 Arlington Parade, Brixton Hill, 
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Open Mon to Sat 9am to 6pm 





with the remittance Sina to Intra Press 


















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We stock a large range of electronic 

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11Victoria House, 
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Hanley, 
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PRACTICAL ELECTRONICS AUGUST 1989 


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Resistors 1/4 W 5% carbon (E12) 1p metal fila 1% ....sesssse 


Resistor Pack 85 different E12 values + zero ohm link total co 


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1000 resistors ses SeC er nO ee 2S. b 
LEDs cia ee SISO. eaasssssosscsessseseesesecsnsesrseseeee-Op Cah. Yellow 11 
Cable ties 75mm. ......ssssssseeeee- Lp each £5.95/ 1 000 £49.50 per 10,000 
Stepping motor 4 phase 12v7.5' step 50 OHMS. ...saneesseneneernerdB.95 
SAA1027 stepping motor driver Chip. ..vsssaninssenseusenennennenb 3.99 
FM transmitter Kit good quality sound ......ssusesessesseenseneee £1.94 
High quality photo resist coper clad epoxy glass boards 
Dimensions _ single sided double sided 
3x4 inches £0.69 £0.76 
4x8 inches £1.64 £1.91 
6x12 inches £3.80 
12x12 inches £7.50 

Special Offers 


Computer Grade Capacitors with screw terminals 38000uf 20v £2.50 
8700uf 10v £1.95, €b000uf 15v £2.95, 10000uf 16v £1.50 

7 segment Commom anode led display 12mm ....ssemsenensennen £0.45 
LM2931AT5.0 Low drop out SV regulator T0220 package .......£0.85 
BS250 P channel MOSFET £0.45, BC559 transistor ....£3.95 per 100 
T4LS05 hex inverter £10.00 per 100, used 8748 Microcontroller £3.50 
Stereo LW/MW/FM Tuner pre-amp assembly complete with 
volume/tone controls and tuning scale Brand new in makers carton ..... 
2 cstane bis oiciaoiedenleecsiantinneenidesnawmeeinsnige) 9), (ANY £20 
Circuit diagram description and setting up procedure for tuner 
assembly etal above £0.50. 5 digit 4 electromagnetic ar r 


Hour counter (used) 7 digit mains 240V AC SOHZ .......sss..ssese+»+£0.95 

LCD display 16 digit 7x) dots dot matrix ......sssssssessssssrsssesseseses 

Querty keyboard | key good quality SWItCHES .....sssssessssesssessse 
wide range of CMOS TTL 74HC 74F Linear transistors kits 
capacitors, resistors tools etc always in stock 

JPG Electronics 276 Chatsworth Road Chesterfield $40 2BH 

Access orders (0246) 211202. Callers welcome 



































Carbon Film Resistors Y4W E24 series 0:51R to10M0 - 1p 
100 off per value -75p 1000 off in even hundreds per value — £7 
Metal Film VW 10RO to 1MO 5% E12 series — 2p 1% E24 series — 3p 
Watt metal/carbon film E24 series 1R0 to 10M0 — 1%p 
1 Watt metal/carbon film E12 series 4R7 to 10MO — 5p 
BC107/8/9 - 12p BC547/8/9 — 8p BC182L 184L - 10p 
BFY50/51/52 - 20p 2N3055 — 50p TIP31A,32A — 25p TIP,41,42, - 40p 


Tantalum head subminiature electrolytics (Mids/Volts) . 

0-1/35, 0:22/35, 0-47/35, 3-3/16, 4-7/16 - 14p 4-7/35 — 15p 
2:2/35, 4-7/25, 10/5-15p  4-7/35, 6/8/16 -16p = — 10/16, 22/6 - 20p 
22/16 — 30p 33/10 — 30p 47/10 - 35p 100/6 - 40p 


Aluminium Electrolytics (Mids/Volts) 

1/50, 2:2/50, 4-7/25, 4-7/50, 10/16, 10/25, 10/50 — 5p 22/16, 22/25 - 6p 
22/50, 47/16, 47/25, 47/50-6p 100/16, 100/25-7p 100/50 -12p 
100/100 - 14p 220/16 — 8p 220/25, 220/50 - 10p 470/16, 470/25 — 11p 
1000/25 — 18p 1000/35, 220/25 — 22p 4700/25 — 70p 


Miniature Polyester Capacitors 250V Wkg. Vertical Mounting 
01, 015, 022, -033, -047, -068-4p 0-1-5p 0-15, -22-6p 0-47 - 8p 


Mylar Capacitors 100V Wkg. Vertical Mounting E12 Series 
1000p to 8200p -3p -01to-068-4p 0-1-5p 0-15, 0:22 - 6p 


Subminiature Ceramic Plate 100V Wkg. E12 Series Vertical Mounting 
2%o 1P8 to 47P-3p  56Pto330P-4p 10% 390P to 4700P - 4p 
Ceramic plate/disc E6 Series 50V 22P to .047 - 2p 


Polystyrene Capacitors 63V Wkg. E12 Series Axial Mounting 
10P to 820P — 3p 1000P to 10,000 — 4p 12,000P - 5p 
1N4148-2p 1N4002-4p  1N5404-14p WO! bridge - 25p 


0A91 - 6p AA143 - 8p W005 - 20p 1N4006 - 6p 
Zener diodes E24 series 3V3 to 33V 400mW - 8p 1 watt - 12p 
L.E.D’s Red, Green & Yellow 3mm & 5mm - 10p 8mm —- 35p 


20mm fuse 0-1A to 5A quick blow — 5p Anti Surge — 8p 
High Speed drills 08mm, 1-0mm, 1-3mm, 1-5mm, 2mm — 30p 

Expo Reliant drilling machines 12V d.c. with improved 3-jaw chuck 6.50 
Nicads AA - 80p HP11 — £2 PP3 - £4.20 Universal Chargers — £6.50 
Glass reed switches single pole make contacts—8p | Magnets—12p 


VAT inclusive. Return postage 25p (free over £5). Lists free. 
THE C.R. SUPPLY CO., 


127 Chesterfield Road, 
Sheffield S8 ORN. Tel. 557771. 


>>>RESISTOR PACKS<<< 


1/4W 5% CARBON FILM 
E12 RANGE 10R to 10M 
10 OF EACH VALUE 
Total 730 resistors 
£4.95 


Add 25p P&P & 15% VAT 
RMOS P.O. BOX 3 
USK GWENT NP5 2YF. 













TURN YOUR SURPLUS 


ICS transistors etc into cash, immediate 
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Contact: 
COLES-HARDING & CO., 
103 South Brink, Wisbech, Cambs. 
ESTABLISHED 15 YEARS 
Tel:0945 584188 - Fax: 0945 588844 


PRACTICAL ELECTRONICS AUGUST 1989 











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ROBOTICS 


Use your home computer to operate servo based 


Phone 
Richard Caplis 
with your 
classified ad! 


Robots of your own design. Suitable for ZX 
Spectrum, Tatung, Einstein and Amstrad CPC. 
Send SAE for details to: 

PRF Software Dept. PE, 26 Olton Road, 
Mickleover, Derby DE3 5PL. 





Are you an electronics 

hobbyist? 

If so, you will benefit from joining 
British Amateur Electronics Club! 
BAEC, C. Bogod, 26 Forrest Rd., 

Penarth, South Glamorgan 







01-743 8888 


We now accept payment by 
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You can also use PE 
Fax Line: 
01-743-3062 


* up to 1.000 inputs 
* 60+100 mm faders, pots, 
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* 6 auxiliaries Hf — 
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CAMBRIDGE COMPUTER SCIENCE LTD 
































5.25 inch Disk Drives, 80 Track DSDD £34.00 each 
are Dawes, “aT S800 £0800 each SURPLUS/REDUNDANT ELECTRONICS 
5 25" Disk Drives, 80Tk, DSDD Used, No Wty £15.00 each COMPONENTS WANTED 

i Sete ay of 10 : bata ICs - Tuners - Transistors - Valves - Diodes etc - any 
ead enneniae facial ©200 each quantity considered -immediate payment. 

SOW PSU SV 6A, 12V2.54,-SV0.5A,-2V05A £16.00 each ADM ELECTRONICS SUPPLIES 

Bench PSU 0-30V @SA Limited quantity only at £45.00 each Tel 0827 873311 Fax: 0827 874835 
Single Data lead (BBC Micro to Disk Drives) £2.00 each 

Dual Data lead (BBC Micro to 2 Disk Drives) £ 4.00 each 

Power lead (BBC Micro to Disk Drive} £1.00 each 

Dual leads (BBC Micro to 2 Disk Drives) £2.00 each 

68000 CPUs (The first orders get 12MHz chips) £3.50 each 

74LS TTL assortments. 10 different devices £1.20 pack 

8K Byte NV ram chips £3.00 each £10.00 four 


20 pin dil low profile IC sockets £0.50 (ten) - £ 4.00 (100) 
40 pin dil low profile IC sockets £0.60 (ten) - £ 5.00 (100) 
Keyboard, 100 keys on board LCD & micro if £8.00 each 
Toroidal mains transformer 12V 4A & 0.4A, 12-0-12 @0.1A & 2A , 
9-09 @0.2A £4.00 each - £6.00 for 2. - £8.00 for 3 
All items new unless stated . Add 15% VAT to all prices. Prices 
include postage. Add 50p to orders below £5.00. Send an SAE for our 
latest list or for more info. 

Dept PE, 374 Milton Road, Cambridge, CB4 15U 

Tel: 0223 327602 

SAE with all enquiries please! 


Project your component image here! 
Phone PE on 01-743-8888 





J.N. BULL ELECTRICAL 
Please note our correct 
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203500 


Languages, Operating Systems, Graphics, Databases, AI Experts 
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allin 


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The one tool every programmer should have! 


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Essex SS14 4DR 


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OUT 


in display pages of 
PE! Phone Sarah 
Holtham on 


001-743-8888 for details! 















MAKE YOUR OWN PCB's 


Just about everything from polishing blocks to 
plated through hole equipment. 
Very keen prices - discount on quantity. 
S.A.E. for complete price list or telephone: 
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27 North Street, Redruth, Cornwall TR15 tHJ 
Tel: 0209 211050 


THE 








DYNAMO 






a Reviewed in PE. 
January, 1989. £42 
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post. 

(Brochure £3 
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Phone our Advertisement Dept. 
O11. 7 Todd-Forb 
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TECHNICAL INFO SERVICES (PE) 
76 Church St., Larkhall, Lanarkshire ML9 1HE 
Phone 0698 884585 Mon-Fri, 9-5 
any other time 0688 883334 FOR FAST QUOTES 
WORLD'S LARGEST COLLECTION SERVICE MANUALS Most 
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Video Recorders - £12.50 
Most Colour TV, Audio, Test, Vintage, Amateur etc. £6.00 
Please state Make/Model/Type with order. 

FREE Catalogue Unique Repair and Data Guides with all 
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MAURITON ELECTRONICS LTD (PE), 

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a AMATEUR 
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FOR FULL DETAILS SEND S.A.E TO: 


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56 


STREET Crs 














HOMEBUILT | 


by Alfred T. Forbes 
ISBN 0-9597749-0-4 


enquiries welcome. 











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NEW VHF MICROTRANSMITTER KIT, tuneable 
80-115 MHz, 500 metre range, sensitive electret 
microphone, high quality PCB. SPECIAL OFFER 
complete kit ONLY £5 or assembled and ready 
to use £8.95. POST FREE. Access orders 
telephone 021 411 1821. Cheques/ P.O.'s to: 
Quantek Electronics Ltd, (Dept P.E.), 45a 
Station Road, Northfield, Birmingham, B31 
3TE 

Surveillance devices, lasers, Tesla coils, 
scramblers, ultrasonic and many more, 
over 150 designs. Send SAE to: 
Plancentre, Old Wharf, Dynock Road, 
Ledbury HR8 2HS 

KITS MICROTRANSMITTER, VHF/FM, 
received on standard radio, 25x15mm, free 
microphone included - £4.50. Telephone 
transmitter, amazingly uses no batteries - 
£5.49. Bleeper transmitter vhf - £8.59 inc 
p&p. SAE list. Remittance to: A.C.E. (PE), 
99 Greenheath, Hednesford, Staffs. - 


MISCELLANEOUS 


Laboratory stock clearence equipment, 


computers, ECG transducers, Geigers, 
anemometers, spare motors etc. SAE list. 
Laboratories, Maplehurst, RH13 6LL Tel: 
0403 891 236 

0) ! Use Practical 
Electronics classified pages for your small 
ads. For details phone Richard Caplis on 
01-743-8888. 
Small Press monthly - the guide to what 
is happening in the Small Press world. 
Latest issue out now. 50p (plus 20p p&p or 
A5 SAE): SPG, BM BOZO, London WC1N 
3XX ( Full address). 
Hightemp Super Conductors. Kit of all 
chemicals needed plus instructions. Send 
cheque/PO for £10 to: P. Catania, 15 
Llanvair Drive, Ascot, Berks SL5 9HS. 
VOICE/SOUND activated switches easy 
to follow diagrams and uses only £10.00. 
Components and P.C.Bs available: 
Herrington, 63 Home Farm Road, Hanwell, 
London W7 iNL. 
Had a good idea? Ideas, designs and 
inventions wanted. S.A.E. for more 
information: Martin Bliss Prop. MD, Adapta 
Plan, Dept. PE, 28 Clerkenwell Crescent, 
Malvern, Worcs WR14 2TX. | 

| 








rf unt SRAMS/DRAM 

Surplus stock - Tel:Roger/ Sue on 01- 
336-1104 
IMPORTANT - Does anyone know the 
whereabouts of MARK HUNT ( ex. M. 
Plaquets & Riverside Studios). Please 
contact BOB WEBB on 01-675-0335, 

olar Eclipse 22nd Ju Q -FIN 
For your travel and accomodation needs 
phone Margaret at Salford Travel Agency 
on 061-8329131. ABTA members. We are 
Finland specialists. Other holidays 
available. 


PRACTICAL ELECTRONICS AUGUST 1989 


















ase Communications Ltd make a 
Cz of telling you proudly that all 

employees in their Watford, Herts, 
electronics factory have free access to 
computer terminals. To what extent this is 
utilised in the manufacturing processes I 
don't really know, but it certainly has 
interesting social implications. 

The company makes data communications 
equipment — modems, concentrators, multi- 
plexers, switching systems and the like. It 
also builds local-area and other datacoms 
networks for customers. You may 
remember that it got into the news a few 
months ago during Mr. Gorbachev's short 
visit to the UK. The Soviet president had 
_asked to see a_ highly automated 
manufacturing plant while he was here. 
Lord Young, the DTI minister, took him to 
Case, partly because it is near London but 
mainly because the factory acts as a 
Government demonstration site for showing 






















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particular observation has been borne out 
by events. Over two centuries it has been 
seen working through  industrialisation 
(concentration of manufacturing), mechani- 


sation and computer-based automation. 


More than ten years ago the National 
Computing Centre concluded from a case 
study that the introduction of a computer- 
based system in a factory "can change 
roles" in ways that cause workers to form 
different attitudes to their tasks and to the 
management. Now that CIM has developed 
a lot more it has become the subject of 
deeper analysis. In the USA, for example, 
Professor Shoshana Zuboff has shown in a 
recent book (Jn the age of the smart 
machine’) that IT is progressively changing 
the meaning of work, the identities of 
workers and people's sense of themselves. 

She says this is happening because IT cuts 
right across the traditional hierarchy of 
factory organisation. In the past managerial 


CIM AND SOCIETY 







the application of computer-aided design 
(CAD) and testing and computer integrated 
manufacturing (CIM). 

Case are using CIM for much the same 
reason as other manufacturers. There is 
pressure on them from their owners, the 
shareholders of the Dowty group, to sell 
their products at a good profit to keep up 
group dividends and stock market value. 
This means being able to sell the products 
at competitive prices, which in turn means 
manufacturing efficiently to keep the 
production cost of individual items (unit 
costs) to a minimum. 

Basically this is done by reducing waste 
— of time and materials. Individual 
processes — like component insertion in 
pcbs, flow soldering, board testing — are 
already speeded up by automatic machines. 
But there is still a possibility of waste 
occurring between these processes. In 
manufacturing generally this takes the 
forms of excessive inventory, work-in- 
progress and setting-up times, and rejected 
items and reworking. By integrating all the 
separate processes into a smooth overall 
flow without bottlenecks a company can 
minimise these sources of waste. _ 

Nowadays this integration is achieved 
through the use of computer systems. CIM 
forms a bridge between CAD, the planning 
of manufacturing resources and individual 
computer-controlled machines (CAM — 
computer aided manufacturing). And here 
the 'manufacturing’ in CIM embraces the 
complete range of a company's activities — 
specification, design, buying components 
and materials, assembly, testing and 
despatch out of the factory gates. 

There is a continual exchange of data 
between the individual computer-controlled 
processes and a central database, allowing 
integration of the various business 
management tasks such as procurement, 
stock-keeping, marketing and accounting. 


PRACTICAL ELECTRONICS AUGUST 1989 


BY TOM IVALL 


Full Marx, Karl - 
the manager shall 
sit down with the 
workers, and the 

worker with the 

machine | 





Using CIM reduces both the product 
development time and the time from the 
receipt of orders to the despatch of goods. 

In discussing last month the possible 
impact of artificial intelligence (AI) on our 
lives I was really jumping the gun a bit. AI 
technology, which is largely based on non- 
numerical or symbolic computing, is farther 
into the future than current information 
technology (IT), which in the main uses 
conventional numerical computing. In fact 
IT is already affecting our lives, in the 
various ways I've been mentioning in 
previous reports over the years. 

CIM is a particular application of IT 
which is likely to influence our lives not 
merely by its immediate effects on the kind 
of work done in factories but by modifying 
the very structure of industrialised societies. 
Way back in the Victorian era Karl Marx 
said that when new production technology 
comes into conflict with the existing social 
relations of production the conditions are 
set for social change. Whatever you think of 
Marxism as a political ideology, this 


power to order things and people has rested 
on the distinction that managers do mental 
work (making decisions etc), which is mainly 
carried out through communication with 
people, while factory operatives do largely 
manual work on objects. CIM is changing 
this organisational structure by making the 
work on objects more mental than manual. 

All the hard graft and even the skill 
content is being provided by software- 
controlled machines. Information, no longer 
the exclusive property of managers, is made 
available to workers through vdu screens of 
computer terminals instead of being 
accepted through spoken or written forms 
of communication. 

This new structure, according to 
Professor Zuboff, encourages employees to 
take initiatives on the basis of information 
supplied by the computer terminals, rather 
than passively waiting for instructions from 
the managers. It will lead to more open and 
participative ways of working. But she also 
thinks it will require a lot of psychological 
adjustment. People won't want to give up 
the traditional idea of management being 
achieved by instruction and command 
through a hierarchy of distributed power, 
from the top down. 

Already the old Victorian concept of the 
manager as a boss who tells you what to do is 
going out. Increasingly the manager is being 
seen not as a superior who sits above you but 
as a professional who sits beside you. The 
Japanese express it openly by dressing 
managers and workers in the same uniforms. 

Undoubtedly CIM will accelerate this 
new trend in the social relations of the 
factory. But the ways we relate to each other 
anywhere are partly influenced by our 
occupations, and how these are perceived in 
the general pattern of an industrialised 
culture. So the effects of the new production 
technologies will certainly be reflected in 
the structure of society at large. PPE] 


57 














PRACTICAL ELECTRONICS 
BOOK SERVICE 


Here ts your Editor's choice of books he 
thinks will be of interest to 
electronics and 
computer enthusiasts 


BEGINNERS AND EARLY STARTERS 


NWIEW Mini-Matrix Board Projects. 
R.A.Penfold. 112 pages. £2.50. 
Order Code BP99 


Shows a selection of 20 useful and interesting circuits 
that can be built on a mini-matrix board of 24 holes by 10 
copper strips in size - an ideal book for early 
experimenters. 


Wie W From Atoms to Amperes. 
F.A.Wilson. 160 pages. £2.95. 
Order Code BP254. 


For the absolute beginner, clearly explaining the 
fundamentals behind the whole subject of electricity and 
electronics. 


WIEW Electronic Projects for 
Beginners. 

F.G.Rayer. 128 pages. £1.95. 
Order Code BP48 


Specially for the newcomer to electronics who is looking 
for a book containing a wide range of easily made projects. 
Some circuits need no soldering and many others show 
actual component and wiring layouts. 


Electronics Build and Learn 
R.A.Penfold. 128 Pages. £5,95. 
Order Code PC 101 


Combining theory and practice, the book describes a 
circuit demonstrator unit that is used in subsequent 
chapters to introduce common electronic components and 
circuit concepts, complete with practical experiments. 








Practical Electronic Building Blocks 
R.A.Penfold. There are two books - 
Book 1 : 128 pages. £1.95. 

Order Code BP117 

Book 2 : 112 pages. £1.95. 

Order Code BP118 


Book 1 is about oscillators and gives circuits for a wide 
range, including sine, triangle, square, sawtooth and 
pulse waveforms and numerous others from voltage 
controlled to customised ic types. 

Book 2 looks at amplifiers, ranging from low level discrete 
and opamp types to ic power amps. A selection of mixers, 
filters and regulators is included. 


30 Solderless Breadboard Projects 
R.A.Penfold. Two books each of 160 
pages. Book 1 : £2.25. Order Code 
BP107. Book 2 : £2.25. Order Code 
BP113. 


Each project is designed for building on a Verobloc 
breadboard and is accompanied by a description, circuit 
and layout diagrams and relevant constructional notes. 
Many of the components are common to several projects. 
Book 1 covers linear devices, and Book 2 covers cmos 
logic chips. 


Beginners Guide to Building 
Electronic Projects R.A.Penfold. 112 
pages. £1.95. Order Code BP 227 


Shows the complete beginner how to tackle the practical 
side of electronics and includes simple constructional 


projects. 


TEST AND MEASUREMENT 


Getting the Most from Your 
Multimeter 


R.A.Penfold. 112 pages. £2.95. 
Order Code BP239 


There's more to what you can do with a meter than meets 
the casual eye. The book covers the basics of what you 
can do with analogue and digital meters and discusses 
component and circuit testing. 


NWIEW Test Equipment Construction 
R.A. Penfold £2.95. 
Order Code BP248 


Describes in detail how to construct some simple and 
inexpensive, but extremely useful, pieces of test 
equipment. 


58 


Oscilloscopes 
I.Hickman. £6.95. 


Order Code NT3 

Subtitled 'How to Use Them, How They Work’ the book is 
illustrated with diagrams and photographs and is 
essential reading for any one who wants to know about 
scopes, from first principles to practical applications. 


How to Get Your Electronic Projects 
Working. 

R.A.Penfold. 96 pages. £2.50. 

Order Code BP110. 


Essential reading for anyone who wants first-time success 
in project assembly. Covers tracing mechanical faults as 
well as testing for failures of active and passive 
components of most types. 





























SATELLITE TV 


Guide - 2nd edition John Breeds. 
£11.95. Order Code STV1 


Full of vital information for any competent diyer who 
wishes to install a satellite tv antenna and obtain 
optimum reception quality. 


An Introduction to Satellite 
Television 

F.A.Wilson. 112 pages. £5.95. 
Order Code BP195 


Informative answers to many of the questions about 
this communications revolution. The information is 
presented on two levels, one aimed at the complete 
beginner, the other at professional engineers and 


serious amateur enthusiasts. 


eNO D) (OPW IPB LER (6 






§ Vig 
I. Sinclair. 112 padee: £5.95. 
Order Code PC102 


A non-mathematical introduction to the new digital 
technology, discussing the principles and methods 
involved in devices such as cd, dat and sampling. 










Electronic Music Projects 
R.A.Penfold. 112 pages. £2.50. 
Order Code BP74 


24 practical constructional projects covering fuzz, wah, 
sustain, reverb, phasing, tremolo etc. The text is split into 
four sections covering guitar, general, sound generation 
and accessory projects. 











More Advanced Electronic Music 
Projects 

R.A.Penfold. 96 pages. £2.95. 
Order Code BP174 


Complementing BP74 by covering more advanced and 
complex projects including flanging, chorus, ring 
modulation, plus a selection of drum, cymbal and gong 
circuits. 















NW Computer Music Projects 
R.A.Penfold. 112 pages. £2.95. 
Order Code BP173 


Shows how home computers can produce electronic music 
and covers sequencing, analogue and Midi interfacing, 
digital delay lines and sound generators. 














Practical Midi Handbook 
R.A.Penfold. 160 pages. £5.95. 
Order Code PC103 


A practical how-to-do-it book for musicians and 
enthusiasts who want to exploit the capabilities of Midi. 
Covers keyboards, drums, sequencers, effects, mixers, 
guitars, and computer music software. 













Midi Projects 
R.A.Penfold. 112 pages. £2.95. 
Order Code BP182 


Practical details of interfacing many popular home 
computers with Midi systems, and also covering Midi 
interfacing to analogue and percussion synths. 














NEW Electronic Synthesiser 
Construction. 

R.A.Penfold. 112 pages. £2.95. 
Order Code BP185. 


Even relative beginners should find the monophonic 
synthesiser described here within their capabilities if the 
book is thoroughly read. Individual aspects of the synth 
are dealt with separately and pcb designs are shown for 
the main modules. 

















PRACTICAL ELECTRONICS AUGUST 1989 












DIGITAL AND COMPUTING 


wisWw A Concise Introduction to MS- 
DOS. 

N. Kantaris. 64 pages. £2.95. 

Order Code BP232 


A ready-reference guide for those who need a quick insight 
into the essential command functions of this operating 
system, but who don't have the time to learn it fully. 


An Introduction to Computer 
Peripherals , 

R.A. and J.W. Penfold. 80 pages. 
£2.50. Order Code BP170 


Covers such items as monitors, printers, disc drives, 
cassettes, modems, etc, explaining what they are and how 
to use them with your computer and with each other. 


Microprocessing Systems and 
Circuits 

F.A.Wilson. 256 pages. £2.95. 
Order Code BP77 


A comprehensive guide to the elements of microprocessing 
systems, covering the fundamental principles behind this 
important subject. 


Introduction to 6800/6802 
Microprocessor Systems 
R.J.Simpson and T.J.Terrell. 238 
pages. £10.95. Order Code NT9 


The book covers systems hardware, programming 
concepts and practical experimental work that will assist 
in understanding the 6800/6802 microprocessor, with 
additional information on the 6802D5E evaluation 
system. 


NEW An Introduction to 68000 
Assembly Language. 

R.A. and J.W.Penfold. 112 pages. 
£2.95. Order Code BP184 


Covers the fundamentals of writing programs that will 
vastly increase the speed of 68000 based machines such 
as the Commodore Amiga, Atari ST range, Apple 
Mackintosh, etc. 








Getting the Most from Your Printer 
J.W.Penfold. 96 pages. £2.95. 
Order Code BP181 


How to use the features found on most dot-matrix printers 
from programs and popular wordprocessors, showing 
examples of what must be typed to achieve a given effect. 









Micro Interfacing Circuits 
R.A.Penfold. Two books, each of 112 
pages. 

Book 1 : £2.25.Order Code BP130. 
Book 2 : £2.25. Order Code BP131 


Both books include practical circuits and useful 
background information though pcb layouts are not 
included. Book 1 mainly covers computer input-output 
techniques. Book 2 deals primarily with practical 
application circuits. 


WEeW An Introduction to 6502 
Machine Code. 

R.A. and R.W. Penfold. 112 pages. 
£2.50. Order Code BP147 


Covers the main principles of machine code programming 
on 6502-based machines such as the Vic-20, Oric- 
1/Atmos, Electron, BBC and Commodore 64. It assumes 
no previous knowledge of microprocessors or machine 
code and gives illustrative programming examples. 


WIEW A Z-80 Workshop Manual. 
E.A.Parr. 192 pages. £3.50. 


Order Code BP112 

A book for those who already know Basic but wish to 
explore machine code and assembly language 
programming on Z80 based computers. 


Practical Digital Electronics 
Handbook 

M.Tooley. 208 pages. £6.95. 
Order Code PC 104 


Nine constructional projects introduce digital circuits, 
logic gates, timers, microprocessors, memory and interface 
circuits - an essential book for anyone interested in digital 
devices. : 





a 


GENE. CONSTRUCTIONAL 


NEW Electronic Science Projects. 
Owen Bishop. 144 pages. £2.95. 
Order Code BP104 


A bumper bundle of experimental projects ranging in 
complexity and including a colour temperature meter, 
electronic clock, a solid state (led display) scope, an infra- 
red laser, a fascinating circuit for measuring the earth's 
electrical field strength, and many more. 


Electronic Security Devices 
R.A.Penfold. 112 pages. £2.50. BP56 


Full of ideas for keeping your valuables safe. The circuits 
include designs for light, infra-red, ultrasonic, gas, smoke, 
flood, door and baby sensors. 


NEW More Advanced Electronic 
Security Projects. R.A.Penfold. 112 
pages. £2.95. Order Code BP190 


Follows on from where BP56 leaves off and describes a 
number of more up-to-date and sophisticated projects, 
such as pyro-sensors, infra-red and doppler-shift 
detection, fibre-optic loops, and many others. 


Wis W_Electronic Projects for Cars 
and Boats. 

R.A.Penfold. 96 pages. £1.95. 
Order Code BP94 


PRACTICAL ELECTRONICS AUGUST 1989 


1 y simple projects that can 
and/or boat. Stripboard constructional details are 
included, as are explanations of the circuit theory. 


Power Supply Projects 
R.A.Penfold. 96 pages. £2.50. 
Order Code BP76 


A selection of power supply designs, including simple 
unstabilised, fixed voltage regulated and variable voltage 
stabilised, ni-cad charger, voltage step-up, and inverter. 


More Advanced Power Supply 
Projects 

R.A.Penfold. 96 pages. £2.95. 
Order Code BP192 


Covers more advanced topics than BP76 and includes 
precision supplies, switch mode and computer controlled 
supplies, plus a selection of miscellaneous circuits. 


NSW_Popular Electronic Circuits. 
R.A.Penfold. 160 pages. £2.95. 


Order Code BP80 


Containing a wide range of circuit designs for experienced 
constructors who are capable of producing working 
projects direct from a circuit diagram without specific 
constructional details. 
















DATA AND INFORMATION BOOKS 


Digital IC Equivalents anc 
Connections 
A.Michaels. 320 pages. £5.95. 
Order Code BP140 

Linear IC Equivalents and Pin 
Connections 

A.Michaels. 256 pages. £5.95. 
Order Code BP141 


Between them these two books show equivalents and pin 
connections of a popular user-orientated selection o 
European, American and Japanese ics. They also 
include details of functions, manufacturer and country 
of origin. The Digital ICs book also quotes details o 
packaging and families. 
































Opamps 
B.Dance. £6.50. 
Order CodeNT2 





Electronic Hobbyists Handbook 
R.A.Penfold. 96 pages. £4.95. Order 


enthusiast is likely to need for day-to-day pursuance o 
hobby electronics. 


Practical Electronics Handbook 
I. Sinclair. £7.95. 


Order Code NT1 


A useful and carefully selected collection of standard 
circuits, rules-of-thumb and design data for enthusiasts, 
students and engineers involved in radio, computing and 
general electronics 





Newnes Electronics Pocket Book 
LE.Parr. £6.95. 


Order Code NT10 
Presents all aspects of modem electronics in a readable 
and largely non-mathematical style, and is a good source 
of valuable information for enthusiasts and professional 
engineers alike. 





G.C. Loveday. £6.95. 
Order Code BM 101 


Tackles the problems of designing circuits from scratch, 
introducing the concept of target specifications, the 
design sequence, device selection, rules of thumb, and 
useful equivalent circuits. 









59 











READY-MADE 
P.C. BOARDS 


Simplify your project assembly — use a ready-made printed 
circuit board. All are fully drilled and roller tinned. Just slot in 
the components as shown in the project texts, and solder them. 
PCBs are the professional route to project perfection. 


MAIL ORDERING 


Select the boards you want, and send your order to 
PE PCB SERVICE, PRACTICAL ELECTRONICS, 
193 UXBRIDGE ROAD, LONDON W12 9RA. 
Prices include VAT and postage and packing. Add £2 per board 


for overseas airmail. Cheques should be crossed and made 
payable to Intra Press. 

Quote the project name and PCB Code Number, and print 
your name and address in Block Capitals. Do not send any 
other correspondence with your order. 


TELEPHONE ORDERS (OPEN 24 HOURS) 


Use your Access card and phone your order to 


0268 289923 


clearly stating your name and address, card number, and 
order details. 


All orders receive priority attention, but allow 28 days for 
delivery in case a PCB is temporarily out of stock. 
WE CAN ONLY SUPPLY THE PCBS LISTED HERE 
CHECK LATEST ISSUE FOR 
PRICES BEFORE ORDERING 


































PHOTOCOPIES OFTHE TEXTS MAY BE BOUGHT FROM THE 
EDITORIAL OFFICE AT £1.00 EACH PART (£1.50 OVER- 
SEAS), P&P INCLUSIVE. 

COMPONENTS ARE AVAILABLE FROM ADVERTISERS. 


“DEC 86 oe = ae _ an ss 0) ns i Ss 1s i ee a 
VIDEO ENHANCER manual acuta . yo ee 
video imp rovement._ 





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= oscilloscop pe add-on ce estrge : 







: G GCSE ECHPROCESS( IT ue are delay a _ 
FUNGEN-— triple waveform signal generator © 
LIGHT CONTROLLER — delayed switching 

















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60 . - PRACTICAL ELECTRONICS AUGUST 1989 





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"PB COMPETITION __| 








SHARPEN UP YOUR 
LIFE-STYLE! 


WIN THE NEW 
SHARP IQ-7000 
PERSONAL 
ORGANISER! 


THREE TO BE WON - 
EACH WORTH £170! 


With 32KB memory, the Sharp IQ-7000 
electronic personal organiser could 
transform your private or business life. 
Direct keyboard access to : 

199 year calendar Diary and 
appointments book. World clock for 212 
cities. Multifunction calculator. 200+ 
entry phone and address directory. 12 
page memo and report pad. 

And its functions can be expanded using 
additional slot-in ic cards available from 
Sharp stockists - PC compatible interface, 
8-language translator, Thesaurus, spell 
checker, etc. (Additional cards not 
included in prize award.) 













HOW TO ENTER: 


Your Editor sometimes gets carried away with puns 
and word relationships - putting his unaided IQ to 
erroneous use he spotted relationships between 
author's surnames in this month's issue and the 
phrases in the box. Write alongside each phrase the 
author's surname you think is most appropriate. All 
correct entries will be put in a draw to take place on 
31st August 1989, the first three names drawn will 
each win a Sharp IQ-7000 Organiser! 12 month's free 
subscription to PE will go to the next three names 
drawn. The Editor's decision is final! 





SHARP IQ-7000 ENTRY FORM 











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PRACTICAL ELECTRONICS AUGUST 1989 


61 














RECORD LED 















MICROPHONE 


AMP 


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MMH 






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of kitchen scales. A low cost digital ruler 
could also be made. 

Gol Su (ibes ane ese de etieos £6.50 


SN 


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VOICE RECORD/PLAYBACK KIT 










This simple to construct and even simpler to operate kit will record and playback 
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Interak 1 

























tell you? 


obsolescence at bay. 


system CP/M Plus. 


you out of a jam if you get into one. 


in 1970. 
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INTERAK can be commenced with the minimum of outlay. Bare boards 
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Made for those who must know what goes inside. Full circuit diagrams 


and descriptions are provided. And honestly, can you really use a 
computer effectively if you don't know what's inside and nobody will 


Solid engineering construction — something to be proud of. 19” 3U rack 
mounting, plug in circuit boards and modular construction keeps 


Flourishing Independent Users Group, and newsletter. Hundreds of 
programs on disk at little or no cost from the Users Group. 


Program in machine code (Assembler), Basic, “C”, Forth, etc Database, 
Word Processing, Scientific applications. 


Cassette tape operation or disk (up to 4 drives, 1 Megabyte 3.5” available 
from us, but you can add 3”, 5.25”, 8” if you want). Disk operating 
64K RAM, Z80 based at present with potential for expansion to a 16 
Megabytes address space and Zilog's latest Z80280 in the future. 
Needs no specialised knowledge to construct, and we will happily get 
Availability of personal and individual after sales service, impossible to 
obtain from large companies, who are only after your money. 


Security of supply — from Greenbank Electronics, established 













For more details write or phone us: 
Greenbank Electronics, Dept (E6P), 460 New Chester Road, 
Rock Ferry, Birkenhead, Merseyside. L42 2AE. Tel: 051-645 3391 


VARIABLE VOLTAGE TRANSFORMERS 


INPUT 220/240V AC 50/60 OUTPUT 0-260V 

200W 0.1 amp max £24.00 p&p £3.00 (£31.05 inc VAT) 

0.5KVA 2.5 amp max £26.50 £3.75 (£34.79 inc VAT) 
1KVA 5ampmax £34.00 £4.25 (£43.99 inc VAT) 
2KVA10ampmax £49.00 £5.50 (£62.68 inc VAT) 
3KVA15ampmax £65.00 £6.25 (£81.94 inc VAT) 
5KVA 25 amp max £115.00 

Carriage on request 


VOLTAGE CHANGING 

TRANSFORMER q 

1250 Watt auto. Tapped 0-90V, 100, 110, 115, 
120, twice to obtain voltages between 90 
and 240V. Fitted in heavy duty louvered 
metal case. Fused input. Price incl VAT & 
p&p £39.50. 


COMPREHENSIVE RANGE OF TRANSFORMERS-LT- 
ISOLATION & AUTO (110-240V Auto transfer either 
cased with American socket and mains lead or open 
frame type. Available for immediate delivery. 


ULTRA VIOLET BLACK LIGHT FLUORESCENT TUBES 
Aft 40 watt £10.44 (£12.00 inc VAT) Caller only 
2ft 20 watt £7.44 + £1.25 p&p (£9.99 inc VAT) 

13in 10 watt £5.80 + 75p p&p (£7.53 inc VAT) 

12in 8 watt £4.80 + 75p p&p (£6.38 inc VAT) 
Yin 6 watt £3.60 + 50p p&p (£5.12 inc VAT) 
6in 4 watt £3.60 + 50p p&p (£5.12 inc VAT) 
230V AC BALLAST KIT for either 6in, 9in or 

12in tubes £5.50 + 55p p&p (£6.96 inc VAT) 

For 13in tubes £6.00 + 75p p&p 

(£7.75 inc VAT) 


400 WATT UV LAMP 
Only £28.00 + £2.50 p&p (£35.08 inc VAT) 


175 WATT SELF BALLASTED BLACK LIGHT 
MERCURY BULBS Available with BC or ES 
fitting. Price incl VAT & p&p £18.65. 


12 VOLT BILGE PUMPS 

Buy direct from the importers 

500 GPH 15ft head 3 amp 

£16.00 inc. 

1750 GPH 15ft head 9 amp 

£19.25 + £2.00 p&p (£25.00 inc VAT) 

EPROM ERASURE KIT ———— 
Build your own EPROM ERASURE for a fraction of 
the price of a made-up unit kit of parts less case 
includes 12in 8 watt 2537 Angst Tube Ballast unit 
pair of bi-pin leads neon indicator on/off switch 
safety microswitch and circuit £14.00 + £2.00 p&p 
(£18.40 inc VAT) 


SUPER HY-LIGHT STROBE KIT 

Designed for Disco, Theatrical users etc. 

Approx 16 joules. Adjustable speed £48.00 + £2.00 p&p 
(£57.50 inc. VAT) 

Case and reflector £22.00 + £2.00 p&p (£27.60 inc VAT) 
SAE for further details including Hy-Light and 
industrial Strobe Kits. 


Ample 
Parking Space 


Showroom open 
Monday/Friday 


PRACTICAL ELECTRONICS AUGUST 1989 





WIDE RANGE OF XENON FLASHTUBES 


Write/Phone your enquires 


SOLID STATE RELAY 


Single make will switch up to 250 V AC 10 amp. 
operating voltage 3-32 V DC silent contactless opto- 
isolated. Fraction of maker's price £3.00 + 50 p p+p. 
Total inc VAT £4.03. 


SPECIAL OFFER AC CAPACITORS 

1.5 MFD 440V £2.00 5 MFD 440V £4.00 

2 MFD440V £2.50 5.4 MFD 280V £2.00 

4.1 MFD 440V £3.50 5 MED 660V £3.00 
12 MFD 400 £4.00 

p+p 50p per unit plus VAT to be added to total. 


TORIN CENTRIFUGAL BLOWER 

230V ac 2,800 RPM 0.9amp 130mm diameter impellor 
outlet 63 x 37mm overall size 195 x 160 x 150mm long. 
Price £17.50 + £2.50 p&p (£23 inc. VAT) 


SHADED POLE GEAR MOTORS 

In the following sizes: 

9 RPM 12 RPM 80 RPM 160 RPM 110V AC or 240V AC 
with capacitors (supplied). Price incl VAT & p&p £12.65 


GEARED MOTORS 

71 RPM 20lb inch torque reversable 115V AC input 
including capacitor and transformer for 240V AC 
operation. Price incl VAT & p&p £23.00. 


12 V DC COOLER EXTRACTOR FAN 
New brushless motor 92mm sq. Price incl VAT & p&p 
£11.50. 


SOLID STATE EHT UNIT 
Input 230/240V AC, Output approx 15KV. Producing 
10mm spark. Built-in 10 sec timer. Easily modified 
for 20 sec, 30 sec to continuous. Designed for boiler 
ignition. Dozens of uses in the field of physics and 
electronics. eg supplying neon or argon tubes etc. 
Price less case £8.50 + £1.00 p&p (£10.93 inc VAT) NMS 


COOLING FANS-BRAND NEW! 

200/400V AC American Boxer ‘Peewee’ 7-bladed high 
efficiency cooling unit 80mm sq zx 40mm deeps 40cm 
approx. Price incl VAT & p&p £10.35. 


EX-EQUIPMENT FANS 120mm sq x 38mm deep in 
either 115V or 230V AC Tested and guaranteed. Price 
incl VAT & p&p £7.76. 


Large selection of various speed greased motors from 
stock. Phone or write for details. 


From stock at prices that defy competition 


C/F Blowers Program Timers 
Microswitches Synch Motors 
write/phone your enquiries 


NMS = NEW MANUF SURPLUS 
R&T = RECONDITIONED AND TESTED 


SERVICE TRADING CO 


57 BRIDGMAN ROAD, CHISWICK, LONDON W4 5BB EN 
: 


01-995 1560 
ACCOUNT CUSTOMERS MIN. ORDER £10 













ede m= |OUDSPEAKERS-19 INCH STEREO RACK AMPLIFIERS LARGE S.A.E., 30p STAMPED FOR CURRENT LIST. 


Wiesel ace a elala.me)e\U Mats) | Supplied ready built and tested. OMP VARISPEED TURNTABLE CHASSIS. 






















OMP POWER AMPLIFIER MODULES now enjoy a world-wide reputation for quality, reliability and 
performance at a realistic price. Four models available to suit the needs of the professional and hobby market, i.e., Industry, . Eo ee ih i  afen Come he 1 
Leisure, Instrumental and Hi-Fi etc. When comparing prices, NOTE all models include Toroidal power supply, Integral heat sink, | : ee DRIVEN DC MOTOR 3 TRANSIT SCREWS 3 12” DIE CAST PLATTER 3 
Glass fibre P.C.B., and Drive circuits to power compatible Vu meter. Open and short circuit proof. Ro. . NEON STROBE %* CALIBRATED BAL WEIGHT 9% REMOVABLE HEAD 
THOUSANDS OF MODULES PURCHASED BY PROFESSIONAL USERS SHELL %& ‘%"CARTRIDGE FIXINGS % CUE LEVER *& POWER 220/240V 
cs 390x305mm %& SUPPLIED WITH MOUNTING CUT-OUT 
OMP100 Mk 11 Bi-Polar Output power 110 watts a 
R.M.S. into 4 ohms, Frequency Response 15Hz -— — PRICE £59.99 + £3.50 P&P. 
« 30KHz —3aB, T.H.D. 0.01%, S.N.R. —118dB, Sens. for  Meyaire VM Ven a ilemer\ahasl els 
~ Max. output 500mV at 10K, Size 355 x 115x65mm. STANTON AL500 GOLDRING G850 
PRICE £33.99 + £3.00 P&P. PRICE £16.99 + 50p P&P PRICE £6.99 + 50p P&P 





NEW SERIES Il MOS-FET MODULES ro) foam (esse ol oem ZO) tow 1m iat-e THOUSANDS PURCHASED 
OMP/MF 100 Mos-Fet Output power 110 watts R.M.S. MiG LaliMONAU=ts RRUAOR Cla NIN = SL RINGmalccugs BY PROFESSIONAL USERS 
into 4 ohms, Frequency Response 1Hz — 100KHz Beier - 
~3dB, Damping Factor, >300, Slew Rate 45V/uS, _ 
T.H.D. Typical 0.002%, Input Sensitivity 500mV, S.N.R. | 
—125dB. Size 300 x 123 x 60mm. oe 
PRICE £39.99 + £3.00 P&P. : : 


—— ane nenanemannd 


OMP/MF200 Mos-Fet Output power 200 watts R.M.S. 
into 4 ohms, Frequency Response 1Hz — 100KHz 
—3dB, Damping Factor >300, Slew Rate 50V/uS, 
T.H.D. Typical 0.001%, Input Sensitivity 500mV, S.N.R. 
—130dB. Size 300 x 155 x 100mm. 

PRICE £62.99 + £3.50 P&P. 


& 


NEW MXF SERIES OF POWER AMPLIFIERS 
THREE MODELS:— MXF200 (100w + 100w) 





OMP/MF300 Mos-Fet Output power 300 watts R.M.S. 


into 4 ohms, Frequency Response 1Hz - 100KHz MXF400 (200w + 200w) MXF600 (300w + 300w) 
* —3dB, Damping Factor >300, ses Rate oh All power ratings R.M.S. into 4 ohms. 
* T.H.D. Typical 0.0008%, Input Sensitivity SOOMV, f ee aryReEs: x Inde ies wi | 
, : pendent power supplies with two Toroidal Transformers * Twin L.E.D. Vu meters * Rotary 
S.N.R. —1300B. Size 330 x 175 x 100mm. indended level controls * Illuminated on/off switch * XLR connectors * Standard 775mV inputs * Open and short 


PRICE £79.99 + £4.50 P&P. circuit proof * Latest Mos-Fets for stress free power delivery into virtually any load * High slew rate * Very low 
; distortion x Aluminium cases * MXF600 Fan Cooled with D.C. Loudspeaker and Thermal Protection. 
NOTE:— MOS-FET MODULES ARE AVAILABLE IN TWO VERSIONS, STANDARD — INPUT SENS, 500mV BAND WIDTH 100KHz. 


NEC (PROFESSIONAL EQUIPMENT COMPATABLE) — INPUT SENS, 775mV, BAND WIDTH SOKHz, ORDER STANDARD OR PEC fj USED THE WORLD OVER IN CLUBS, PUBS, CINEMAS, DISCOS ETC. 
SIZES:— MXF 200 W19”xH312" (2U)xD11" 

_ Vu METER Compatible with our four amplifiers detailed above. A very accurate visual MXF 400 W19"H51%" (3U) x D12” 
© display employing 11 L.E.D. diodes (7 green, 4 red) plus an additional on/off indicator. MXF 600 W19"H5'%" (3U) x D13” 
Sophisticated logic control circuits for very fast rise and decay times. Tough moulded plastic MXF200 £171.35 


case, with tinted acrylic front. Size 84 x 27 x 45mm. PRICES: MXF400 £228.85 


PRICE £8.50 + 50p P&P. 
P MXF600 £322.00 
SECURICOR DELIVERY £12.00 EACH 

























= 


LOUDSPEAKERS 






OMP LINNET LOUDSPEAKERS OMP SLIDE DIMMER 
LARGE SELECTION OF SPECIALIST LOUDSPEAKERS 1K WATT & 2.5K WATT 
AVAILABLE, INCLUDING CABINET FITTINGS, SPEAKER THE VERY BEST IN QUALITY AND VALUE pearance ae a 
GRILLES, CROSS-OVERS AND HIGH POWER, HIGH FRE- ™ ee SUITABLE FOR RESISTIVE AND INDUC: 
MADE ESPECIALLY TO SUIT 
QUENCY BULLETS AND HORNS, LARGE S.A.E. (30p § = Fa TODAY'S NEED FOR COM- BE ADILY FLUSH MOUNTED TFRCUGK 
STAMPED) FOR COMPLETE LIST. 4 PACTNESS WITH HIGH OUTPUT PANEL/CABINET CUT-OUTS, ADVANCED 
SOUND LEVELS, FINISHED IN FEATURES INCLUDE:— 
McKENZIE:— INSTRUMENTS, P.A., DISCO, ETC. HARDWEARING BLACK VYNIDE . 
ALL McKENZIE UNITS 8 OHMS IMPEDENCE ee ee oe 
8” 100 WATT C8100GPM GEN. PURPOSE, LEAD GUITAR, EXCELLENT MID., DISCO. is, INCORPORATES 12” DRIVER PLUS Seon 
RES, FREQ, 80Hz. FREQ, RESP, TO 14KHz. SENS, 99dB. ..........0-00---0-o PRICE £28.59 + £2.00 P&P. : HIGH FREQ. HORN FOR FULL a 
10” 100 WATT C10100GP GUITAR, VOICE, ORGAN, KEYBOARD, DISCO, EXCELLENT MID. FREQ. RANGE: 45Hz-20KHz BOTH : MeN QBanDICAlan 
RES, FREQ, 70Hz. FREQ, RESP, TO 6KHz. SENS, 1004B. .............-.-...2-0+-. PRICE £34.70 + £2.50 P&P. MODELS 8 OHM, SIZE H18” x W15” * FLASH OVERRIDE 
10” 200 WATT C10200GP GUITAR, KEYBOARD, DISCO, EXCELLENT HIGH POWER MID. x D12". a BUTTON 
RES, FREQ, 45Hz. FREQ, RESP, TO 7KHz. SENS, 103QB. .......2...-00-00000- PRICE £47.48 + £2.50 P&P. Se * HIGH & LOW LEVEL 
12” 100 WATT C12100GP HIGH POWER GEN, PURPOSE, LEAD GUITAR, DISCO. CHOICE OF TWO MODELS | PRESETS 
RES, FREQ, 45Hz. FREQ, RESP, TO 7KHz. SENS, 98@B. ..........-.0-.000--oe PRICE £36.66 + £3.50 P&P. < * FULLY SUPPRESSED 
12” 100 WATT C12100TC TWIN CONE) HIGH POWER WIDE RESPONSE, P.A., VOICE, DISCO. POWER RATINGS QUOTED IN WATTS RMS FOR EACH CABINET tons 600 
RES, FREQ, 45Hz. FREQ, RESP, TO 14KHz. SENS, He | ae £37.63 + £3.50 P&P. 
12” 200 WATT C12200B HIGH POWER BASS, KEYBOARDS, DISCO, P.A. : 99 PER PAIR 
RES. FREQ, 40Hz. FREQ, RESP, TO 7KHz. SENS, 1000B. ............-...0.0-- PRICE £64.17 + £3.50 P&P. OMP 12-100 (100W 100dB) PRICE £159.99 2. 5KW H128xW76xD79mm 
12" 300 WATT C12300GP HIGH POWER BASS LEAD GUITAR, KEYBOARDS, DISCO, ETC. ore OMP 12-200 (200W 102dB) PRICE £209.99 PER PAIR piece. uses 
RES, FREQ, 45Hz. FREQ, RESP, TO 5KHz. SENS, 1000B. ...........2.02.000 PRI 5.79 + £3. = : 
15” 100 WATT C15100BS BASS GUITAR, LOW FREQUENCY, P.A., DISCO. cease ence SECURICOR DEL.:— £12.00 PER PAIR 2.5K WATT £24.99 + 60p P&P 
RES, FREQ, 40Hz. FREQ. RESP, TO 5KHz. SENS, 98dB. ........2..2.0:0 ICE £53.70 + £4. 
15” 200 WATT C15200BS VERY HIGH POWER BASS. PIEZO ELECTRIC TWEETERS-MOTOROLA 
RES, FREQ, 40Hz. FREQ, RESP, TO 4KHz. SENS, 99@B. ........-.00.000 ee PRICE £73.26 +£4.00P&P. ff PIEZO ELECTRIC TWEETERS — MOTOROLA 
15” 250 WATT C15250BS VERY HIGH POWER BASS. Join the Piezo revolution. The low dynamic mass (no voice coil) of a Piezo tweeter produces an improved transient 
RES, FREQ, 40Hz. FREQ. RESP, TO 4KHz. SENS, 990B. PRICE £80.53 + £4.50 P&P. response with a lower distortion level than ordinary dynamic tweeters. As a crossover is not required these units can 
15” 400 WATT C15400BS VERY HIGH POWER, LOW FREQUENCY BASS. be added to existing speaker systems of up to 100 watts (more if 2 put in series). FREE EXPLANATORY LEAFLETS 
RES, FREQ, 40Hz. FREQ, RESP, TO 4KHz. SENS, 102B. ............-0.--0---: PRICE £94.12 +£4.50P&P. Bf ciopi icp wiTH EACH TWEETER 
18” 400 WATT C18404BS EXTREMELY HIGH POWER, LOW FREQUENCY BASS. TYPE ‘A’ (KSN2036A) 3” round with protective wire 
RES, FREQ, 27Hz. FREQ, RESP, TO 3KHz. SENS, QOGB. .................. eee PRICE £167.85 + £5.00 P&P. mesh, ideal for bookshelf and medium sized Hi-fi 


speakers. Price £4.90 each + 50p P&P. 

TYPE ‘B’ (KSN1005a) 312” super horn. For general 
purpose speakers, disco and P.A. systems etc. Price 
£5.00 each + 50p P&P. 

TYPE ‘C’ (KSN6016A) 2” x5” wide dispersion horn. For 
quality Hi-fi systems and quality discos etc. Price £6.99 
each + 50p P&P. 


EARBENDERS:— HI-FI, STUDIO, IN-CAR, ETC. 


ALL EARBENDER UNITS 8 OHMS EXCEPT EB8-50 AND EB10-50 DUAL 4 AND 8 OHM. 
BASS, SINGLE CONE, HIGH COMPLIANCE, ROLLED FOAM SURROUND 

8” 50 WATT EB8-50 DUAL IMPEDENCE, TAPPED 4/8 OHM BASS, HI-FI, IN-CAR. 

RES, FREQ, 40Hz. FREQ, RESP, TO7KHZ SENS: 87D. vi cessestusscrceiensrncoesten: PRICE £8.90 + £2.00 P&P. 
10” 50 WATT EB10-50 DUAL IMPEDENCE, TAPPED 4/8 OHM BASS, HI-FI, IN-CAR. 


RES, FREQ, 40HZ. FREQ, RESP, TO 5KHz. SENS, IS case cteancensecc encanta: : : F , 1 BM ag ; 

10” 100 WATT EB10-100 BASS, Her et aod PRICESIE00S £200 P er TYPE ‘D’ (KSN1025A) 2”x6" wide dispersion horn. 
RES, FREQ, 35Hz. FREQ, RESP, TO 3KHz. SENS, 960B. «0.0.0... PRICE £27.50 + £3.50 P&P. Upper frequency response retained extending down to 
12” 60 WATT EB12-60 BASS, HI-FI, STUDIO. mid range (2KHz). Suitable for high quality Hi-fi systems 


and quality discos. Price £9.99 each + 50p P&P. 
TYPE ‘E’ (KSN1038A) 3%” horn tweeter with attractive 
silver finish trim. Suitable for Hi-fi monitor systems etc. 
Price £5.99 each + 50p P&P. 

LEVEL CONTROL Combines on a recessed mounting 


RES, FREQ, 28Hz. FREQ; RESP, TO SKHz. SENS, 920B. ..265:00..siecsesssmsnivses PRICE £21.00 + £3.00 P&P. 
12” 100 WATT EB12-100 BASS, STUDIO, HI-Fl, EXCELLENT DISCO. 

RES, FREQ, 26Hz, FREQ, RESP, TOSKHz. SENS, S3d0B)......csissescesseases ccezacs PRICE £32.00 + £3.50 P&P. 
FULL RANGE TWIN CONE, HIGH COMPLIANCE, ROLLED SURROUND 

5." 60 WATT EB5-60TC (TWIN CONE) HI-FI, MULTI-ARRAY DISCO ETC. 





















RES, FREQ, 63Hz. FREQ, RESP, TO 20KHz. SENS, 92dB. ...seecc0c cscs PRICE £9.99 + £1.50 P&P. eet iauk ice coche 
612” 60 WATT EB6-60TC (TWIN CONE) HI-FI, MULTI-ARRAY DISCO ETC. ee ee es eee 

RES. FREQ, 38Hz. FREQ, RESP, TO 20KHz. SENS, 94€B. «oo... cece PRICE £10.99 + £1.50 P&P. 

8” 60 WATT EB8-60TC (TWIN CONE) HI-Fi, MULTI-ARRAY DISCO ETC. 

RES. FREQ, 40Hz. FREQ, RESP. TO 18KHz. SENS, 890B. ....-0.-.0sscccccccue PRICE £12.99 + £1.50 P&P. STEREO DISCO MIXER 

10’ 60 WATT EB10-60TC (TWIN CONE) HI-FI, MULTI-ARRAY DISCO ETC. | 

RES, FREQ, 35Hz. FREQ, RESP, TO 12KHz. SENS, 86dB. ......0..0...eee PRICE £16.49 +£2.00P&P. | STEREO DISCO MIXER with 2 x SbandL &R 


graphic equalisers and twin 10 segment L.E.D. 

Vu Meters. Many outstanding features 5 Inputs 

with individual faders providing a useful com- 

bination of the following:— 

3 Turntables (Mag). 3 Mics. 4 Line including CD 

plus Mic with talk over switch Headphone Moni- ~ 
~ 




















TRANSMITTER HOBBY KITS 


PROVEN TRANSMITTER DESIGNS INCLUDING GLASS FIBRE 
PRINTED CIRCUIT BOARD AND HIGH QUALITY COMPONENTS 
COMPLETE WITH CIRCUIT AND INSTRUCTIONS 
















tor. Pan Pot L. & R. Master Output controls. 
Output 775mV. Size 360 x280x90mm. Supply 
220-240v. 















3W FM TRANSMITTER 80-108MHz, VARICAP CONTROLLED PROFESSIONAL PER- 


FORMANCE, RANGE UP TO 3 MILES, SIZE 38 x 123mm, SUPPLY 12V @ 0.5AMP, 2 ST 


PRICE £14.49 + £1.00 P&P 3 watt FM Price £134.99 -—— £4.00 P&P ESS 
FM MICRO TRANSMITTER (BUG) 100-108MHz VARICAP TUNED COMPLETE WITH Transmitter 
VERY SENS FET MIC, RANGE 100-300m, SIZE 56 x 46mm, SUPPLY 9V BATT, PRICE 






£8.62 + £1.00 P&P 






#B. K. ELECTRONICS cece: 


Ca Tee Ronee OTe DaCeS MELIGNEOPYAT SHLESCOUNER UNIT 5. COMET WAY, SOUTHEND-ON-SEA, ESSEX. SS2 6TR 
VISA ACCESS ACCEPTED BY POST, PHONE OR FAX. ‘\ewanosma TEL: 0702-527572 FAX: 0702-420243 










RACTICAL ELECTRONICS AUGUST 1989 63 











Precision laboratory oscilloscope. 

3 Channels — 3 Trace. 

Sensitive vertical amplifier 1mV/div allows 
very low level signals to be easily observed. 
150mm rectangular CRT has internal 
graticule to eliminate parallax error. 

X-Y mode allows Lissajous patterns to be 
produced and phase shift measured. 

TV sync separator allows measurement of 
video signals. 

20ns/div sweep rate makes fast signals 
observable. | 

Algebraic operation allows sum or difference 
of Channel | and 2 to be displayed. 

Stable triggering of both channels even with 
different frequencies is easy to achieve. 
S0mV/div output from Ch | available to drive 
external instrument e.g. frequency counter. 
A hold-off function permits triggering of 
complex signals and aperiodic pulse 
waveforms. 3 





Iscilloscope 


As above, but with 40MHz bandwidth and 
super bright 12kV tube even at the highest 
frequencies. This instrument also has a 
delayed sweep time base to provide 
magnified waveforms and accurate time 
interval measurement. Truly superb 
precision instrument. 






Order Coupon Send to P.O. Box 3, Rayleigh, SS6 8LR 


Price 








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Allitems subject to availability. Subject to availability both items will be on sale in 
op our shops in Birmingham, Bristol, Leeds, London, Manchester, Nottingham, 
LGeteete dee 2 ooo at wee eae a we a a we ale ae _ southampton and Southend-on-Sea. 


i 1 

! despatched. PHONE BEFORE 

ow COLLIE; SPMFORSAME l 
rs ACCESS AMEX, VISA oo. ec eceeeeseeseesse, Gelete as required. : -DAY DESPATCH ‘ 

1 Ifordering by Credit Card please Sign ............ccccecccecceecceeceucceucceee ' 

: Expiry date of Credit Card..............cccccsssessecoseccsseccesecascceuscceuecss ' ALL PRICES INCLUDE VAT.